Point cloud data transmission apparatus, point cloud data transmission method, point cloud data reception apparatus, and point cloud data reception method

ABSTRACT

Disclosed herein is a method of transmitting point cloud data. The method may include acquiring point cloud data, encoding geometry information including positions of points of the point cloud data, generating one or more LODs based on the geometry information and selecting one or more neighbor points of each point to be attribute-encoded based on the one or more LODs, wherein the selected one or more neighbor points of each point are located within a maximum neighbor point distance, encoding attribute information of each point based on the selected one or more neighbor points of each point, and transmitting the encoded geometry information, the encoded attribute information, and signaling information.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 17/157,198, filed on Jan. 25, 2021, which claims the benefit of Korean Patent Application No. 10-2020-0044852, filed on Apr. 13, 2020, which is hereby incorporated by reference as if fully set forth herein.

TECHNICAL FIELD

Embodiments relate to a method and apparatus for processing point cloud content.

BACKGROUND

Point cloud content is content represented by a point cloud, which is a set of points belonging to a coordinate system representing a three-dimensional space. The point cloud content may express media configured in three dimensions, and is used to provide various services such as virtual reality (VR), augmented reality (AR), mixed reality (MR), XR (Extended Reality), and self-driving services. However, tens of thousands to hundreds of thousands of point data are required to represent point cloud content. Therefore, there is a need for a method for efficiently processing a large amount of point data.

SUMMARY

An object of the present disclosure devised to solve the above-described problems is to provide a point cloud data transmission device, a point cloud data transmission method, a point cloud data reception device, and a point cloud data reception method for efficiently transmitting and receiving a point cloud

Another object of the present disclosure is to provide a point cloud data transmission device, a point cloud data transmission method, a point cloud data reception device, and a point cloud data reception method for addressing latency and encoding/decoding complexity

Another object of the present disclosure is to provide a point cloud data transmission device, a point cloud data transmission method, a point cloud data reception device, and a point cloud data reception method for improving the compression performance of the point cloud by improving the technique of encoding attribute information of geometry-based point cloud compression (G-PCC).

Another object of the present disclosure is to provide a point cloud data transmission device, a point cloud data transmission method, a point cloud data reception device, and a point cloud data reception method for enhancing compression efficiency while supporting parallel processing of attribute information of G-PCC.

Another object of the present disclosure is to provide a point cloud data transmission apparatus, a point cloud data transmission method, a point cloud data reception apparatus, and a point cloud data reception method for reducing the size of an attribute bitstream and enhancing compression efficiency of attributes by selecting neighbor points used for attribute prediction in consideration of an attribute correlation between points of content when attribute information of G-PCC is encoded.

Another object of the present disclosure is to provide a point cloud data transmission apparatus, a point cloud data transmission method, a point cloud data reception apparatus, and a point cloud data reception method for reducing the size of an attribute bitstream and enhancing compression efficiency of attributes by applying a maximum neighbor point distance and selecting neighbor points used for attribute prediction when attribute information of G-PCC is encoded.

Another object of the present disclosure is to provide is to a point cloud data transmission device, a point cloud data transmission method, a point cloud data reception device, and a point cloud data reception method for efficiently encoding/decoding various types of point cloud data by automatically calculating the maximum neighbor point range according to the density to obtain the maximum neighbor point distance in encoding the attribute information of G-PCC.

Objects of the present disclosure are not limited to the aforementioned objects, and other objects of the present disclosure which are not mentioned above will become apparent to those having ordinary skill in the art upon examination of the following description.

To achieve these objects and other advantages and in accordance with the purpose of the disclosure, as embodied and broadly described herein, a method of transmitting point cloud data may include acquiring point cloud data, encoding geometry information including positions of points of the point cloud data, generating one or more levels of detail (LODs) based on the geometry information and selecting one or more neighbor points of each point to be attribute-encoded based on the one or more LODs, encoding attribute information of each point based on the selected one or more neighbor points of each point, and transmitting the encoded geometry information, the encoded attribute information, and signaling information.

According to an embodiment, the selected one or more neighbor points of each point may be located within a maximum neighbor point distance.

According to an embodiment, the maximum neighbor point distance may be determined based on a base neighbor point distance and a maximum neighbor point range.

According to an embodiment, when the one or more LODs are generated based on an octree, the base neighbor point distance may be determined based on a diagonal distance of one node in a specific LOD.

According to an embodiment, the selecting of the one or more neighbor points may include estimating a density of the point cloud data based on the base neighbor point distance and a diagonal length of a bounding box of the point cloud data, and automatically calculating the maximum neighbor point range according to the estimated density.

According to an embodiment, information related to the maximum neighbor point range may be signaled in the signaling information.

In another aspect of the present disclosure, a point cloud data transmission device may include an acquirer configured to acquire point cloud data, a geometry encoder configured to encode geometry information including positions of points of the point cloud data, and an attribute encoder configured to generate one or more levels of detail (LODs) based on the geometry information, select one or more neighbor points of each point to be attribute-encoded based on the one or more LODs, and encode attribute information of each point based on the selected one or more neighbor points of each point, and a transmitter configured to transmit the encoded geometry information, the encoded attribute information, and signaling information.

According to an embodiment, the selected one or more neighbor points of each point may be located within a maximum neighbor point distance.

According to an embodiment, the maximum neighbor point distance may be determined based on a base neighbor point distance and a maximum neighbor point range.

According to an embodiment, when the one or more LODs are generated based on an octree, the base neighbor point distance may be determined based on a diagonal distance of one node in a specific LOD.

The attribute encoder may estimate a density of the point cloud data based on the base neighbor point distance and a diagonal length of a bounding box of the point cloud data, and automatically calculate the maximum neighbor point range according to the estimated density.

According to an embodiment, information related to the maximum neighbor point range may be signaled in the signaling information.

In another aspect of the present disclosure, a point cloud data reception device may include a receiver configured to receive geometry information, attribute information, and signaling information, a geometry decoder configured to decode the geometry information based on the signaling information, an attribute decoder configured to generate one or more levels of detail (LODs) based on the geometry information, select one or more neighbor points of each point to be attribute-decoded based on the one or more LODs, and decode attribute information of each point based on the selected one or more neighbor points of each point and the signaling information, and a renderer configured to render point cloud data reconstructed based on the decoded geometry information and the decoded attribute information.

According to an embodiment, the selected one or more neighbor points of each point may be located within a maximum neighbor point distance.

According to an embodiment, the maximum neighbor point distance may be determined based on a base neighbor point distance and a maximum neighbor point range.

According to an embodiment, when the one or more LODs are generated based on an octree, the base neighbor point distance may be determined based on a diagonal distance of one node in a specific LOD.

The attribute decoder may estimate a density of the point cloud data based on the base neighbor point distance and a diagonal length of a bounding box of the point cloud data, and automatically calculate the maximum neighbor point range according to the estimated density.

According to an embodiment, the attribute decoder may acquire the maximum neighbor point range from the signaling information.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the disclosure and together with the description serve to explain the principle of the disclosure. In the drawings:

FIG. 1 illustrates an exemplary point cloud content providing system according to embodiments.

FIG. 2 is a block diagram illustrating a point cloud content providing operation according to embodiments.

FIG. 3 illustrates an exemplary process of capturing a point cloud video according to embodiments.

FIG. 4 illustrates an exemplary block diagram of point cloud video encoder according to embodiments.

FIG. 5 illustrates an example of voxels in a 3D space according to embodiments.

FIG. 6 illustrates an example of octree and occupancy code according to embodiments.

FIG. 7 illustrates an example of a neighbor node pattern according to embodiments.

FIG. 8 illustrates an example of point configuration of a point cloud content for each LOD according to embodiments.

FIG. 9 illustrates an example of point configuration of a point cloud content for each LOD according to embodiments.

FIG. 10 illustrates an example of a block diagram of a point cloud video decoder according to embodiments.

FIG. 11 illustrates an example of a point cloud video decoder according to embodiments.

FIG. 12 illustrates a configuration for point cloud video encoding of a transmission device according to embodiments.

FIG. 13 illustrates a configuration for point cloud video decoding of a reception device according to embodiments.

FIG. 14 illustrates an exemplary structure operatively connectable with a method/device for transmitting and receiving point cloud data according to embodiments.

FIG. 15 illustrates an example of a point cloud transmission device according to embodiments.

FIGS. 16A to 16C illustrate an embodiment of partitioning a bounding box into one or more tiles.

FIG. 17 illustrates an example of a geometry encoder and an attribute encoder according to embodiments.

FIG. 18 is a diagram illustrating an example of generating LODs based on an octree according to embodiments.

FIG. 19 is a diagram illustrating an example of arranging points of a point cloud in a Morton code order according to embodiments.

FIG. 20 is a diagram illustrating an example of searching for neighbor points based on LOD according to embodiments.

FIGS. 21A and 21B illustrate examples of point cloud contents according to embodiments.

FIGS. 22A and 22B illustrate examples of an average distance, a minimum distance, and a maximum distance of each point belonging to neighbor point set according to embodiments.

FIG. 23A illustrates an example of acquiring a diagonal distance of an octree node of LOD0 according to embodiments.

FIG. 23B illustrates an example of acquiring a diagonal distance of an octree node of LOD1 according to embodiments.

FIGS. 24A and 24B illustrate examples of a range that may be selected as a neighbor point at each LOD.

FIG. 25 illustrates examples of a base neighbor point distance belonging to each LOD according to embodiments.

FIG. 26 is a flowchart illustrating automatic calculation of the maximum neighbor point range based on the density according to an embodiment of the present disclosure.

FIG. 27 is a flowchart illustrating automatic calculation of the maximum neighbor point range based on the density according to another embodiment of the present disclosure.

FIG. 28 illustrates another example of searching for neighbor points based on LOD according to embodiments.

FIG. 29 illustrates another example of searching for neighbor points based on LOD according to embodiments.

FIG. 30 illustrates an example of a point cloud reception device according to embodiments.

FIG. 31 illustrates an example of a geometry decoder and an attribute decoder according to embodiments.

FIG. 32 illustrates an exemplary bitstream structure for point cloud data for transmission/reception according to embodiments.

FIG. 33 illustrates an exemplary bitstream structure for point cloud data according to embodiments.

FIG. 34 illustrates a connection relationship between components in a bitstream of point cloud data according to embodiments.

FIG. 35 illustrates an embodiment of a syntax structure of a sequence parameter set according to embodiments.

FIG. 36 illustrates an embodiment of a syntax structure of a geometry parameter set according to embodiments.

FIG. 37 illustrates an embodiment of a syntax structure of an attribute parameter set according to embodiments.

FIG. 38 illustrates an embodiment of a syntax structure of a tile parameter set according to embodiments.

FIG. 39 illustrates an embodiment of a syntax structure of geometry slice bitstream( ) according to embodiments.

FIG. 40 illustrates an embodiment of a syntax structure of geometry slice header according to embodiments.

FIG. 41 illustrates an embodiment of a syntax structure of geometry slice data according to embodiments.

FIG. 42 illustrates an embodiment of a syntax structure of attribute slice bitstream( ) according to embodiments.

FIG. 43 illustrates an embodiment of a syntax structure of attribute slice header according to embodiments.

FIG. 44 illustrates an embodiment of a syntax structure of attribute slice data according to embodiments.

FIG. 45 is a flowchart of a method of transmitting point cloud data according to embodiments.

FIG. 46 is a flowchart of a method of receiving point cloud data according to embodiments.

DETAILED DESCRIPTION

Description will now be given in detail according to exemplary embodiments disclosed herein, with reference to the accompanying drawings. For the sake of brief description with reference to the drawings, the same or equivalent components may be provided with the same reference numbers, and description thereof will not be repeated. It should be noted that the following examples are only for embodying the present disclosure and do not limit the scope of the present disclosure. What can be easily inferred by an expert in the technical field to which the present invention belongs from the detailed description and examples of the present disclosure is to be interpreted as being within the scope of the present disclosure.

The detailed description in this present specification should be construed in all aspects as illustrative and not restrictive. The scope of the disclosure should be determined by the appended claims and their legal equivalents, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.

Reference will now be made in detail to the preferred embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. The detailed description, which will be given below with reference to the accompanying drawings, is intended to explain exemplary embodiments of the present disclosure, rather than to show the only embodiments that can be implemented according to the present disclosure. The following detailed description includes specific details in order to provide a thorough understanding of the present disclosure. However, it will be apparent to those skilled in the art that the present disclosure may be practiced without such specific details. Although most terms used in this specification have been selected from general ones widely used in the art, some terms have been arbitrarily selected by the applicant and their meanings are explained in detail in the following description as needed. Thus, the present disclosure should be understood based upon the intended meanings of the terms rather than their simple names or meanings. In addition, the following drawings and detailed description should not be construed as being limited to the specifically described embodiments, but should be construed as including equivalents or substitutes of the embodiments described in the drawings and detailed description.

FIG. 1 shows an exemplary point cloud content providing system according to embodiments.

The point cloud content providing system illustrated in FIG. 1 may include a transmission device 10000 and a reception device 10004. The transmission device 10000 and the reception device 10004 are capable of wired or wireless communication to transmit and receive point cloud data.

The point cloud data transmission device 10000 according to the embodiments may secure and process point cloud video (or point cloud content) and transmit the same. According to embodiments, the transmission device 10000 may include a fixed station, a base transceiver system (BTS), a network, an artificial intelligence (AI) device and/or system, a robot, an AR/VR/XR device and/or server. According to embodiments, the transmission device 10000 may include a device, a robot, a vehicle, an AR/VR/XR device, a portable device, a home appliance, an Internet of Thing (IoT) device, and an AI device/server which are configured to perform communication with a base station and/or other wireless devices using a radio access technology (e.g., 5G New RAT (NR), Long Term Evolution (LTE)).

The transmission device 10000 according to the embodiments includes a point cloud video acquisition unit 10001, a point cloud video encoder 10002, and/or a transmitter (or communication module) 10003.

The point cloud video acquisition unit 10001 according to the embodiments acquires a point cloud video through a processing process such as capture, synthesis, or generation. The point cloud video is point cloud content represented by a point cloud, which is a set of points positioned in a 3D space, and may be referred to as point cloud video data. The point cloud video according to the embodiments may include one or more frames. One frame represents a still image/picture. Therefore, the point cloud video may include a point cloud image/frame/picture, and may be referred to as a point cloud image, frame, or picture.

The point cloud video encoder 10002 according to the embodiments encodes the acquired point cloud video data. The point cloud video encoder 10002 may encode the point cloud video data based on point cloud compression coding. The point cloud compression coding according to the embodiments may include geometry-based point cloud compression (G-PCC) coding and/or video-based point cloud compression (V-PCC) coding or next-generation coding. The point cloud compression coding according to the embodiments is not limited to the above-described embodiment. The point cloud video encoder 10002 may output a bitstream containing the encoded point cloud video data. The bitstream may contain not only the encoded point cloud video data, but also signaling information related to encoding of the point cloud video data.

The transmitter 10003 according to the embodiments transmits the bitstream containing the encoded point cloud video data. The bitstream according to the embodiments is encapsulated in a file or segment (for example, a streaming segment), and is transmitted over various networks such as a broadcasting network and/or a broadband network. Although not shown in the figure, the transmission device 10000 may include an encapsulator (or an encapsulation module) configured to perform an encapsulation operation. According to embodiments, the encapsulator may be included in the transmitter 10003. According to embodiments, the file or segment may be transmitted to the reception device 10004 over a network, or stored in a digital storage medium (e.g., USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc.). The transmitter 10003 according to the embodiments is capable of wired/wireless communication with the reception device 10004 (or the receiver 10005) over a network of 4G, 5G, 6G, etc. In addition, the transmitter may perform a necessary data processing operation according to the network system (e.g., a 4G, 5G or 6G communication network system). The transmission device 10000 may transmit the encapsulated data in an on-demand manner.

The reception device 10004 according to the embodiments includes a receiver 10005, a point cloud video decoder 10006, and/or a renderer 10007. According to embodiments, the reception device 10004 may include a device, a robot, a vehicle, an AR/VR/XR device, a portable device, a home appliance, an Internet of Things (IoT) device, and an AI device/server which are configured to perform communication with a base station and/or other wireless devices using a radio access technology (e.g., 5G New RAT (NR), Long Term Evolution (LTE)).

The receiver 10005 according to the embodiments receives the bitstream containing the point cloud video data or the file/segment in which the bitstream is encapsulated from the network or storage medium. The receiver 10005 may perform necessary data processing according to the network system (for example, a communication network system of 4G, 5G, 6G, etc.). The receiver 10005 according to the embodiments may decapsulate the received file/segment and output a bitstream. According to embodiments, the receiver 10005 may include a decapsulator (or a decapsulation module) configured to perform a decapsulation operation. The decapsulator may be implemented as an element (or component or module) separate from the receiver 10005.

The point cloud video decoder 10006 decodes the bitstream containing the point cloud video data. The point cloud video decoder 10006 may decode the point cloud video data according to the method by which the point cloud video data is encoded (for example, in a reverse process of the operation of the point cloud video encoder 10002). Accordingly, the point cloud video decoder 10006 may decode the point cloud video data by performing point cloud decompression coding, which is the inverse process of the point cloud compression. The point cloud decompression coding includes G-PCC coding.

The renderer 10007 renders the decoded point cloud video data. The renderer 10007 may output point cloud content by rendering not only the point cloud video data but also audio data. According to embodiments, the renderer 10007 may include a display configured to display the point cloud content. According to embodiments, the display may be implemented as a separate device or component rather than being included in the renderer 10007.

The arrows indicated by dotted lines in the drawing represent a transmission path of feedback information acquired by the reception device 10004. The feedback information is information for reflecting interactivity with a user who consumes the point cloud content, and includes information about the user (e.g., head orientation information, viewport information, and the like). In particular, when the point cloud content is content for a service (e.g., self-driving service, etc.) that requires interaction with the user, the feedback information may be provided to the content transmitting side (e.g., the transmission device 10000) and/or the service provider. According to embodiments, the feedback information may be used in the reception device 10004 as well as the transmission device 10000, or may not be provided.

The head orientation information according to embodiments is information about the user's head position, orientation, angle, motion, and the like. The reception device 10004 according to the embodiments may calculate the viewport information based on the head orientation information. The viewport information may be information about a region of a point cloud video that the user is viewing. A viewpoint is a point through which the user is viewing the point cloud video, and may refer to a center point of the viewport region. That is, the viewport is a region centered on the viewpoint, and the size and shape of the region may be determined by a field of view (FOV). Accordingly, the reception device 10004 may extract the viewport information based on a vertical or horizontal FOV supported by the device in addition to the head orientation information. Also, the reception device 10004 performs gaze analysis or the like to check the way the user consumes a point cloud, a region that the user gazes at in the point cloud video, a gaze time, and the like. According to embodiments, the reception device 10004 may transmit feedback information including the result of the gaze analysis to the transmission device 10000. The feedback information according to the embodiments may be acquired in the rendering and/or display process. The feedback information according to the embodiments may be secured by one or more sensors included in the reception device 10004. According to embodiments, the feedback information may be secured by the renderer 10007 or a separate external element (or device, component, or the like).

The dotted lines in FIG. 1 represent a process of transmitting the feedback information secured by the renderer 10007. The point cloud content providing system may process (encode/decode) point cloud data based on the feedback information. Accordingly, the point cloud video decoder 10006 may perform a decoding operation based on the feedback information. The reception device 10004 may transmit the feedback information to the transmission device 10000. The transmission device 10000 (or the point cloud video encoder 10002) may perform an encoding operation based on the feedback information. Accordingly, the point cloud content providing system may efficiently process necessary data (e.g., point cloud data corresponding to the user's head position) based on the feedback information rather than processing (encoding/decoding) the entire point cloud data, and provide point cloud content to the user.

According to embodiments, the transmission device 10000 may be called an encoder, a transmitting device, a transmitter, a transmission system, or the like, and the reception device 10004 may be called a decoder, a receiving device, a receiver, a reception system, or the like.

The point cloud data processed in the point cloud content providing system of FIG. 1 according to embodiments (through a series of processes of acquisition/encoding/transmission/decoding/rendering) may be referred to as point cloud content data or point cloud video data. According to embodiments, the point cloud content data may be used as a concept covering metadata or signaling information related to the point cloud data.

The elements of the point cloud content providing system illustrated in FIG. 1 may be implemented by hardware, software, a processor, and/or a combination thereof.

FIG. 2 is a block diagram illustrating a point cloud content providing operation according to embodiments.

The block diagram of FIG. 2 shows the operation of the point cloud content providing system described in FIG. 1 . As described above, the point cloud content providing system may process point cloud data based on point cloud compression coding (e.g., G-PCC).

The point cloud content providing system according to the embodiments (for example, the point cloud transmission device 10000 or the point cloud video acquisition unit 10001) may acquire a point cloud video (20000). The point cloud video is represented by a point cloud belonging to a coordinate system for expressing a 3D space. The point cloud video according to the embodiments may include a Ply (Polygon File format or the Stanford Triangle format) file. When the point cloud video has one or more frames, the acquired point cloud video may include one or more Ply files. The Ply files contain point cloud data, such as point geometry and/or attributes. The geometry includes positions of points. The position of each point may be represented by parameters (for example, values of the X, Y, and Z axes) representing a three-dimensional coordinate system (e.g., a coordinate system composed of X, Y and Z axes). The attributes include attributes of points (e.g., information about texture, color (in YCbCr or RGB), reflectance r, transparency, etc. of each point). A point has one or more attributes. For example, a point may have an attribute that is a color, or two attributes that are color and reflectance.

According to embodiments, the geometry may be called positions, geometry information, geometry data, or the like, and the attribute may be called attributes, attribute information, attribute data, or the like.

The point cloud content providing system (for example, the point cloud transmission device 10000 or the point cloud video acquisition unit 10001) may secure point cloud data from information (e.g., depth information, color information, etc.) related to the acquisition process of the point cloud video.

The point cloud content providing system (for example, the transmission device 10000 or the point cloud video encoder 10002) according to the embodiments may encode the point cloud data (20001). The point cloud content providing system may encode the point cloud data based on point cloud compression coding. As described above, the point cloud data may include the geometry and attributes of a point. Accordingly, the point cloud content providing system may perform geometry encoding of encoding the geometry and output a geometry bitstream. The point cloud content providing system may perform attribute encoding of encoding attributes and output an attribute bitstream. According to embodiments, the point cloud content providing system may perform the attribute encoding based on the geometry encoding. The geometry bitstream and the attribute bitstream according to the embodiments may be multiplexed and output as one bitstream. The bitstream according to the embodiments may further contain signaling information related to the geometry encoding and attribute encoding.

The point cloud content providing system (for example, the transmission device 10000 or the transmitter 10003) according to the embodiments may transmit the encoded point cloud data (20002). As illustrated in FIG. 1 , the encoded point cloud data may be represented by a geometry bitstream and an attribute bitstream. In addition, the encoded point cloud data may be transmitted in the form of a bitstream together with signaling information related to encoding of the point cloud data (for example, signaling information related to the geometry encoding and the attribute encoding). The point cloud content providing system may encapsulate a bitstream that carries the encoded point cloud data and transmit the same in the form of a file or segment.

The point cloud content providing system (for example, the reception device 10004 or the receiver 10005) according to the embodiments may receive the bitstream containing the encoded point cloud data. In addition, the point cloud content providing system (for example, the reception device 10004 or the receiver 10005) may demultiplex the bitstream.

The point cloud content providing system (e.g., the reception device 10004 or the point cloud video decoder 10005) may decode the encoded point cloud data (e.g., the geometry bitstream, the attribute bitstream) transmitted in the bitstream. The point cloud content providing system (for example, the reception device 10004 or the point cloud video decoder 10005) may decode the point cloud video data based on the signaling information related to encoding of the point cloud video data contained in the bitstream. The point cloud content providing system (for example, the reception device 10004 or the point cloud video decoder 10005) may decode the geometry bitstream to reconstruct the positions (geometry) of points. The point cloud content providing system may reconstruct the attributes of the points by decoding the attribute bitstream based on the reconstructed geometry. The point cloud content providing system (for example, the reception device 10004 or the point cloud video decoder 10005) may reconstruct the point cloud video based on the positions according to the reconstructed geometry and the decoded attributes.

The point cloud content providing system according to the embodiments (for example, the reception device 10004 or the renderer 10007) may render the decoded point cloud data (20004). The point cloud content providing system (for example, the reception device 10004 or the renderer 10007) may render the geometry and attributes decoded through the decoding process, using various rendering methods. Points in the point cloud content may be rendered to a vertex having a certain thickness, a cube having a specific minimum size centered on the corresponding vertex position, or a circle centered on the corresponding vertex position. All or part of the rendered point cloud content is provided to the user through a display (e.g., a VR/AR display, a general display, etc.).

The point cloud content providing system (for example, the reception device 10004) according to the embodiments may secure feedback information (20005). The point cloud content providing system may encode and/or decode point cloud data based on the feedback information. The feedback information and the operation of the point cloud content providing system according to the embodiments are the same as the feedback information and the operation described with reference to FIG. 1 , and thus detailed description thereof is omitted.

FIG. 3 illustrates an exemplary process of capturing a point cloud video according to embodiments.

FIG. 3 illustrates an exemplary point cloud video capture process of the point cloud content providing system described with reference to FIGS. 1 to 2 .

Point cloud content includes a point cloud video (images and/or videos) representing an object and/or environment located in various 3D spaces (e.g., a 3D space representing a real environment, a 3D space representing a virtual environment, etc.). Accordingly, the point cloud content providing system according to the embodiments may capture a point cloud video using one or more cameras (e.g., an infrared camera capable of securing depth information, an RGB camera capable of extracting color information corresponding to the depth information, etc.), a projector (e.g., an infrared pattern projector to secure depth information), a LiDAR, or the like. The point cloud content providing system according to the embodiments may extract the shape of geometry composed of points in a 3D space from the depth information and extract the attributes of each point from the color information to secure point cloud data. An image and/or video according to the embodiments may be captured based on at least one of the inward-facing technique and the outward-facing technique.

The left part of FIG. 3 illustrates the inward-facing technique. The inward-facing technique refers to a technique of capturing images a central object with one or more cameras (or camera sensors) positioned around the central object. The inward-facing technique may be used to generate point cloud content providing a 360-degree image of a key object to the user (e.g., VR/AR content providing a 360-degree image of an object (e.g., a key object such as a character, player, object, or actor) to the user).

The right part of FIG. 3 illustrates the outward-facing technique. The outward-facing technique refers to a technique of capturing images an environment of a central object rather than the central object with one or more cameras (or camera sensors) positioned around the central object. The outward-facing technique may be used to generate point cloud content for providing a surrounding environment that appears from the user's point of view (e.g., content representing an external environment that may be provided to a user of a self-driving vehicle).

As shown in FIG. 3 , the point cloud content may be generated based on the capturing operation of one or more cameras. In this case, the coordinate system may differ among the cameras, and accordingly the point cloud content providing system may calibrate one or more cameras to set a global coordinate system before the capturing operation. In addition, the point cloud content providing system may generate point cloud content by synthesizing an arbitrary image and/or video with an image and/or video captured by the above-described capture technique. The point cloud content providing system may not perform the capturing operation described in FIG. 3 when it generates point cloud content representing a virtual space. The point cloud content providing system according to the embodiments may perform post-processing on the captured image and/or video. In other words, the point cloud content providing system may remove an unwanted area (for example, a background), recognize a space to which the captured images and/or videos are connected, and, when there is a spatial hole, perform an operation of filling the spatial hole.

The point cloud content providing system may generate one piece of point cloud content by performing coordinate transformation on points of the point cloud video secured from each camera. The point cloud content providing system may perform coordinate transformation on the points based on the coordinates of the position of each camera. Accordingly, the point cloud content providing system may generate content representing one wide range, or may generate point cloud content having a high density of points.

FIG. 4 illustrates an exemplary point cloud video encoder according to embodiments.

FIG. 4 shows an example of the point cloud video encoder 10002 of FIG. 1 . The point cloud video encoder reconstructs and encodes point cloud data (e.g., positions and/or attributes of the points) to adjust the quality of the point cloud content (to, for example, lossless, lossy, or near-lossless) according to the network condition or applications. When the overall size of the point cloud content is large (e.g., point cloud content of 60 Gbps is given for 30 fps), the point cloud content providing system may fail to stream the content in real time. Accordingly, the point cloud content providing system may reconstruct the point cloud content based on the maximum target bitrate to provide the same in accordance with the network environment or the like.

As described with reference to FIGS. 1 to 2 , the point cloud video encoder may perform geometry encoding and attribute encoding. The geometry encoding is performed before the attribute encoding.

The point cloud video encoder according to the embodiments includes a coordinate transformer (Transform coordinates) 40000, a quantizer (Quantize and remove points (voxelize)) 40001, an octree analyzer (Analyze octree) 40002, and a surface approximation analyzer (Analyze surface approximation) 40003, an arithmetic encoder (Arithmetic encode) 40004, a geometric reconstructor (Reconstruct geometry) 40005, a color transformer (Transform colors) 40006, an attribute transformer (Transform attributes) 40007, a RAHT transformer (RAHT) 40008, an LOD generator (Generate LOD) 40009, a lifting transformer (Lifting) 40010, a coefficient quantizer (Quantize coefficients) 40011, and/or an arithmetic encoder (Arithmetic encode) 40012.

The coordinate transformer 40000, the quantizer 40001, the octree analyzer 40002, the surface approximation analyzer 40003, the arithmetic encoder 40004, and the geometry reconstructor 40005 may perform geometry encoding. The geometry encoding according to the embodiments may include octree geometry coding, direct coding, trisoup geometry encoding, and entropy encoding. The direct coding and tri soup geometry encoding are applied selectively or in combination. The geometry encoding is not limited to the above-described example.

As shown in the figure, the coordinate transformer 40000 according to the embodiments receives positions and transforms the same into coordinates. For example, the positions may be transformed into position information in a three-dimensional space (for example, a three-dimensional space represented by an XYZ coordinate system). The position information in the three-dimensional space according to the embodiments may be referred to as geometry information.

The quantizer 40001 according to the embodiments quantizes the geometry information. For example, the quantizer 40001 may quantize the points based on a minimum position value of all points (for example, a minimum value on each of the X, Y, and Z axes). The quantizer 40001 performs a quantization operation of multiplying the difference between the minimum position value and the position value of each point by a preset quantization scale value and then finding the nearest integer value by rounding the value obtained through the multiplication. Thus, one or more points may have the same quantized position (or position value). The quantizer 40001 according to the embodiments performs voxelization based on the quantized positions to reconstruct quantized points. The voxelization means a minimum unit representing position information in 3D space. Points of point cloud content (or 3D point cloud video) according to the embodiments may be included in one or more voxels. The term voxel, which is a compound of volume and pixel, refers to a 3D cubic space generated when a 3D space is divided into units (unit=1.0) based on the axes representing the 3D space (e.g., X-axis, Y-axis, and Z-axis). The quantizer 40001 may match groups of points in the 3D space with voxels. According to embodiments, one voxel may include only one point. According to embodiments, one voxel may include one or more points. In order to express one voxel as one point, the position of the center point of a voxel may be set based on the positions of one or more points included in the voxel. In this case, attributes of all positions included in one voxel may be combined and assigned to the voxel.

The octree analyzer 40002 according to the embodiments performs octree geometry coding (or octree coding) to present voxels in an octree structure. The octree structure represents points matched with voxels, based on the octal tree structure.

The surface approximation analyzer 40003 according to the embodiments may analyze and approximate the octree. The octree analysis and approximation according to the embodiments is a process of analyzing a region containing a plurality of points to efficiently provide octree and voxelization.

The arithmetic encoder 40004 according to the embodiments performs entropy encoding on the octree and/or the approximated octree. For example, the encoding scheme includes arithmetic encoding. As a result of the encoding, a geometry bitstream is generated.

The color transformer 40006, the attribute transformer 40007, the RAHT transformer 40008, the LOD generator 40009, the lifting transformer 40010, the coefficient quantizer 40011, and/or the arithmetic encoder 40012 perform attribute encoding. As described above, one point may have one or more attributes. The attribute encoding according to the embodiments is equally applied to the attributes that one point has. However, when an attribute (e.g., color) includes one or more elements, attribute encoding is independently applied to each element. The attribute encoding according to the embodiments includes color transform coding, attribute transform coding, region adaptive hierarchical transform (RAHT) coding, interpolation-based hierarchical nearest-neighbor prediction (prediction transform) coding, and interpolation-based hierarchical nearest-neighbor prediction with an update/lifting step (lifting transform) coding. Depending on the point cloud content, the RAHT coding, the prediction transform coding and the lifting transform coding described above may be selectively used, or a combination of one or more of the coding schemes may be used. The attribute encoding according to the embodiments is not limited to the above-described example.

The color transformer 40006 according to the embodiments performs color transform coding of transforming color values (or textures) included in the attributes. For example, the color transformer 40006 may transform the format of color information (for example, from RGB to YCbCr). The operation of the color transformer 40006 according to embodiments may be optionally applied according to the color values included in the attributes.

The geometry reconstructor 40005 according to the embodiments reconstructs (decompresses) the octree and/or the approximated octree. The geometry reconstructor 40005 reconstructs the octree/voxels based on the result of analyzing the distribution of points. The reconstructed octree/voxels may be referred to as reconstructed geometry (restored geometry).

The attribute transformer 40007 according to the embodiments performs attribute transformation to transform the attributes based on the reconstructed geometry and/or the positions on which geometry encoding is not performed. As described above, since the attributes are dependent on the geometry, the attribute transformer 40007 may transform the attributes based on the reconstructed geometry information. For example, based on the position value of a point included in a voxel, the attribute transformer 40007 may transform the attribute of the point at the position. As described above, when the position of the center of a voxel is set based on the positions of one or more points included in the voxel, the attribute transformer 40007 transforms the attributes of the one or more points. When the trisoup geometry encoding is performed, the attribute transformer 40007 may transform the attributes based on the trisoup geometry encoding.

The attribute transformer 40007 may perform the attribute transformation by calculating the average of attributes or attribute values of neighboring points (e.g., color or reflectance of each point) within a specific position/radius from the position (or position value) of the center of each voxel. The attribute transformer 40007 may apply a weight according to the distance from the center to each point in calculating the average. Accordingly, each voxel has a position and a calculated attribute (or attribute value).

The attribute transformer 40007 may search for neighboring points existing within a specific position/radius from the position of the center of each voxel based on the K-D tree or the Morton code. The K-D tree is a binary search tree and supports a data structure capable of managing points based on the positions such that nearest neighbor search (NNS) can be performed quickly. The Morton code is generated by presenting coordinates (e.g., (x, y, z)) representing 3D positions of all points as bit values and mixing the bits. For example, when the coordinates representing the position of a point are (5, 9, 1), the bit values for the coordinates are (0101, 1001, 0001). Mixing the bit values according to the bit index in order of z, y, and x yields 010001000111. This value is expressed as a decimal number of 1095. That is, the Morton code value of the point having coordinates (5, 9, 1) is 1095. The attribute transformer 40007 may order the points based on the Morton code values and perform NNS through a depth-first traversal process. After the attribute transformation operation, the K-D tree or the Morton code is used when the NNS is needed in another transformation process for attribute coding.

As shown in the figure, the transformed attributes are input to the RAHT transformer 40008 and/or the LOD generator 40009.

The RAHT transformer 40008 according to the embodiments performs RAHT coding for predicting attribute information based on the reconstructed geometry information. For example, the RAHT transformer 40008 may predict attribute information of a node at a higher level in the octree based on the attribute information associated with a node at a lower level in the octree.

The LOD generator 40009 according to the embodiments generates a level of detail (LOD). The LOD according to the embodiments is a degree of detail of point cloud content. As the LOD value decrease, it indicates that the detail of the point cloud content is degraded. As the LOD value increases, it indicates that the detail of the point cloud content is enhanced. Points may be classified by the LOD.

The lifting transformer 40010 according to the embodiments performs lifting transform coding of transforming the attributes a point cloud based on weights. As described above, lifting transform coding may be optionally applied.

The coefficient quantizer 40011 according to the embodiments quantizes the attribute-coded attributes based on coefficients.

The arithmetic encoder 40012 according to the embodiments encodes the quantized attributes based on arithmetic coding.

Although not shown in the figure, the elements of the point cloud video encoder of FIG. 4 may be implemented by hardware including one or more processors or integrated circuits configured to communicate with one or more memories included in the point cloud content providing apparatus, software, firmware, or a combination thereof. The one or more processors may perform at least one of the operations and/or functions of the elements of the point cloud video encoder of FIG. 4 described above. Additionally, the one or more processors may operate or execute a set of software programs and/or instructions for performing the operations and/or functions of the elements of the point cloud video encoder of FIG. 4 . The one or more memories according to the embodiments may include a high speed random access memory, or include a non-volatile memory (e.g., one or more magnetic disk storage devices, flash memory devices, or other non-volatile solid-state memory devices).

FIG. 5 shows an example of voxels according to embodiments.

FIG. 5 shows voxels positioned in a 3D space represented by a coordinate system composed of three axes, which are the X-axis, the Y-axis, and the Z-axis. As described with reference to FIG. 4 , the point cloud video encoder (e.g., the quantizer 40001) may perform voxelization. Voxel refers to a 3D cubic space generated when a 3D space is divided into units (unit=1.0) based on the axes representing the 3D space (e.g., X-axis, Y-axis, and Z-axis). FIG. 5 shows an example of voxels generated through an octree structure in which a cubical axis-aligned bounding box defined by two poles (0, 0, 0) and (2^(d), 2^(d), 2^(d)) is recursively subdivided. One voxel includes at least one point. The spatial coordinates of a voxel may be estimated from the positional relationship with a voxel group. As described above, a voxel has an attribute (such as color or reflectance) like pixels of a 2D image/video. The details of the voxel are the same as those described with reference to FIG. 4 , and therefore a description thereof is omitted.

FIG. 6 shows an example of an octree and occupancy code according to embodiments.

As described with reference to FIGS. 1 to 4 , the point cloud content providing system (point cloud video encoder 10002) or the octree analyzer 40002 of the point cloud video encoder performs octree geometry coding (or octree coding) based on an octree structure to efficiently manage the region and/or position of the voxel.

The upper part of FIG. 6 shows an octree structure. The 3D space of the point cloud content according to the embodiments is represented by axes (e.g., X-axis, Y-axis, and Z-axis) of the coordinate system. The octree structure is created by recursive subdividing of a cubical axis-aligned bounding box defined by two poles (0, 0, 0) and (2^(d), 2^(d), 2^(d)). Here, 2^(d) may be set to a value constituting the smallest bounding box surrounding all points of the point cloud content (or point cloud video). Here, d denotes the depth of the octree. The value of d is determined in Equation 1. In Equation 1, (x^(int) _(n), y^(int) _(n), z^(int) _(n)) denotes the positions (or position values) of quantized points. d=Ceil(Log 2(Max(x _(n) ^(int) ,y _(n) ^(int) ,z _(n) ^(int) ,n=1, . . . ,N)+1))  Equation 1

As shown in the middle of the upper part of FIG. 6 , the entire 3D space may be divided into eight spaces according to partition. Each divided space is represented by a cube with six faces. As shown in the upper right of FIG. 6 , each of the eight spaces is divided again based on the axes of the coordinate system (e.g., X-axis, Y-axis, and Z-axis). Accordingly, each space is divided into eight smaller spaces. The divided smaller space is also represented by a cube with six faces. This partitioning scheme is applied until the leaf node of the octree becomes a voxel.

The lower part of FIG. 6 shows an octree occupancy code. The occupancy code of the octree is generated to indicate whether each of the eight divided spaces generated by dividing one space contains at least one point. Accordingly, a single occupancy code is represented by eight child nodes. Each child node represents the occupancy of a divided space, and the child node has a value in 1 bit. Accordingly, the occupancy code is represented as an 8-bit code. That is, when at least one point is contained in the space corresponding to a child node, the node is assigned a value of 1. When no point is contained in the space corresponding to the child node (the space is empty), the node is assigned a value of 0. Since the occupancy code shown in FIG. 6 is 00100001, it indicates that the spaces corresponding to the third child node and the eighth child node among the eight child nodes each contain at least one point. As shown in the figure, each of the third child node and the eighth child node has eight child nodes, and the child nodes are represented by an 8-bit occupancy code. The figure shows that the occupancy code of the third child node is 10000111, and the occupancy code of the eighth child node is 01001111. The point cloud video encoder (for example, the arithmetic encoder 40004) according to the embodiments may perform entropy encoding on the occupancy codes. In order to increase the compression efficiency, the point cloud video encoder may perform intra/inter-coding on the occupancy codes. The reception device (for example, the reception device 10004 or the point cloud video decoder 10006) according to the embodiments reconstructs the octree based on the occupancy codes.

The point cloud video encoder (for example, the octree analyzer 40002) according to the embodiments may perform voxelization and octree coding to store the positions of points. However, points are not always evenly distributed in the 3D space, and accordingly there may be a specific region in which fewer points are present. Accordingly, it is inefficient to perform voxelization for the entire 3D space. For example, when a specific region contains few points, voxelization does not need to be performed in the specific region.

Accordingly, for the above-described specific region (or a node other than the leaf node of the octree), the point cloud video encoder according to the embodiments may skip voxelization and perform direct coding to directly code the positions of points included in the specific region. The coordinates of a direct coding point according to the embodiments are referred to as direct coding mode (DCM). The point cloud video encoder according to the embodiments may also perform trisoup geometry encoding, which is to reconstruct the positions of the points in the specific region (or node) based on voxels, based on a surface model. The trisoup geometry encoding is geometry encoding that represents an object as a series of triangular meshes. Accordingly, the point cloud video decoder may generate a point cloud from the mesh surface. The direct coding and trisoup geometry encoding according to the embodiments may be selectively performed. In addition, the direct coding and trisoup geometry encoding according to the embodiments may be performed in combination with octree geometry coding (or octree coding).

To perform direct coding, the option to use the direct mode for applying direct coding should be activated. A node to which direct coding is to be applied is not a leaf node, and points less than a threshold should be present within a specific node. In addition, the total number of points to which direct coding is to be applied should not exceed a preset threshold. When the conditions above are satisfied, the point cloud video encoder (or the arithmetic encoder 40004) according to the embodiments may perform entropy coding on the positions (or position values) of the points.

The point cloud video encoder (for example, the surface approximation analyzer 40003) according to the embodiments may determine a specific level of the octree (a level less than the depth d of the octree), and the surface model may be used staring with that level to perform trisoup geometry encoding to reconstruct the positions of points in the region of the node based on voxels (Trisoup mode). The point cloud video encoder according to the embodiments may specify a level at which trisoup geometry encoding is to be applied. For example, when the specific level is equal to the depth of the octree, the point cloud video encoder does not operate in the trisoup mode. In other words, the point cloud video encoder according to the embodiments may operate in the trisoup mode only when the specified level is less than the value of depth of the octree. The 3D cube region of the nodes at the specified level according to the embodiments is called a block. One block may include one or more voxels. The block or voxel may correspond to a brick. Geometry is represented as a surface within each block. The surface according to embodiments may intersect with each edge of a block at most once.

One block has 12 edges, and accordingly there are at least 12 intersections in one block. Each intersection is called a vertex (or apex). A vertex present along an edge is detected when there is at least one occupied voxel adjacent to the edge among all blocks sharing the edge. The occupied voxel according to the embodiments refers to a voxel containing a point. The position of the vertex detected along the edge is the average position along the edge of all voxels adjacent to the edge among all blocks sharing the edge.

Once the vertex is detected, the point cloud video encoder according to the embodiments may perform entropy encoding on the starting point (x, y, z) of the edge, the direction vector (Δx, Δy, Δz) of the edge, and the vertex position value (relative position value within the edge). When the trisoup geometry encoding is applied, the point cloud video encoder according to the embodiments (for example, the geometry reconstructor 40005) may generate restored geometry (reconstructed geometry) by performing the triangle reconstruction, up-sampling, and voxelization processes.

The vertices positioned at the edge of the block determine a surface that passes through the block. The surface according to the embodiments is a non-planar polygon. In the triangle reconstruction process, a surface represented by a triangle is reconstructed based on the starting point of the edge, the direction vector of the edge, and the position values of the vertices. The triangle reconstruction process is performed according to Equation 2 by: i) calculating the centroid value of each vertex, ii) subtracting the center value from each vertex value, and iii) estimating the sum of the squares of the values obtained by the subtraction.

$\begin{matrix} {{\begin{bmatrix} \mu_{x} \\ \mu_{y} \\ \mu_{z} \end{bmatrix}} = {\frac{1}{n}{\sum\limits_{i = 1}^{n}\begin{bmatrix} x_{i} \\ y_{i} \\ z_{i} \end{bmatrix}}}} & \\ {{\begin{bmatrix} {\overset{\_}{x}}_{i} \\ {\overset{\_}{y}}_{i} \\ {\overset{\_}{z}}_{i} \end{bmatrix}} = {\begin{bmatrix} x_{i} \\ y_{i} \\ z_{i} \end{bmatrix} - \begin{bmatrix} \mu_{x} \\ \mu_{y} \\ \mu_{z} \end{bmatrix}}} & \\ {{\begin{bmatrix} \sigma_{x}^{2} \\ \sigma_{y}^{2} \\ \sigma_{z}^{2} \end{bmatrix}} = {\sum\limits_{i = 1}^{n}\begin{bmatrix} {\overset{\_}{x}}_{i}^{2} \\ {\overset{\_}{y}}_{i}^{2} \\ {\overset{\_}{z}}_{i}^{2} \end{bmatrix}}} &  \end{matrix}$

Then, the minimum value of the sum is estimated, and the projection process is performed according to the axis with the minimum value. For example, when the element x is the minimum, each vertex is projected on the x-axis with respect to the center of the block, and projected on the (y, z) plane. When the values obtained through projection on the (y, z) plane are (ai, bi), the value of θ is estimated through a tan 2(bi, ai), and the vertices are ordered based on the value of θ. The table 1 below shows a combination of vertices for creating a triangle according to the number of the vertices. The vertices are ordered from 1 to n. The table 1 below shows that for four vertices, two triangles may be constructed according to combinations of vertices. The first triangle may consist of vertices 1, 2, and 3 among the ordered vertices, and the second triangle may consist of vertices 3, 4, and 1 among the ordered vertices.

TABLE 1 Triangles formed from vertices ordered 1, . . . , n n Triangles 3 (1, 2, 3) 4 (1, 2, 3), (3, 4, 1) 5 (1, 2, 3), (3, 4, 5), (5, 1, 3) 6 (1, 2, 3), (3, 4, 5), (5, 6, 1), (1, 3, 5) 7 (1, 2, 3), (3, 4, 5), (5, 6, 7), (7, 1, 3), (3, 5, 7) 8 (1, 2, 3), (3, 4, 5), (5, 6, 7), (7, 8, 1), (1, 3, 5), (5, 7, 1) 9 (1, 2, 3), (3, 4, 5), (5, 6, 7), (7, 8, 9), (9, 1, 3), (3, 5, 7), (7, 9, 3) 10 (1, 2, 3), (3, 4, 5), (5, 6, 7), (7, 8, 9), (9, 10, 1), (1, 3, 5), (5, 7, 9), (9, 1, 5) 11 (1, 2, 3), (3, 4, 5), (5, 6, 7), (7, 8, 9), (9, 10, 11), (11, 1, 3), (3, 5, 7), (7, 9, 11), (11, 3, 7) 12 (1, 2, 3), (3, 4, 5), (5, 6, 7), (7, 8, 9), (9, 10, 11), (11, 12, 1), (1, 3, 5), (5, 7, 9), (9, 11, 1), (1, 5, 9)

The upsampling process is performed to add points in the middle along the edge of the triangle and perform voxelization. The added points are generated based on the upsampling factor and the width of the block. The added points are called refined vertices. The point cloud video encoder according to the embodiments may voxelize the refined vertices. In addition, the point cloud video encoder may perform attribute encoding based on the voxelized positions (or position values).

FIG. 7 shows an example of a neighbor node pattern according to embodiments.

In order to increase the compression efficiency of the point cloud video, the point cloud video encoder according to the embodiments may perform entropy coding based on context adaptive arithmetic coding.

As described with reference to FIGS. 1 to 6 , the point cloud content providing system or the point cloud video encoder 10002 of FIG. 1 , or the point cloud video encoder or arithmetic encoder 40004 of FIG. 4 may perform entropy coding on the occupancy code immediately. In addition, the point cloud content providing system or the point cloud video encoder may perform entropy encoding (intra encoding) based on the occupancy code of the current node and the occupancy of neighboring nodes, or perform entropy encoding (inter encoding) based on the occupancy code of the previous frame. A frame according to embodiments represents a set of point cloud videos generated at the same time. The compression efficiency of intra encoding/inter encoding according to the embodiments may depend on the number of neighboring nodes that are referenced. When the bits increase, the operation becomes complicated, but the encoding may be biased to one side, which may increase the compression efficiency. For example, when a 3-bit context is given, coding needs to be performed using 2³=8 methods. The part divided for coding affects the complexity of implementation. Accordingly, it is necessary to meet an appropriate level of compression efficiency and complexity.

FIG. 7 illustrates a process of obtaining an occupancy pattern based on the occupancy of neighbor nodes. The point cloud video encoder according to the embodiments determines occupancy of neighbor nodes of each node of the octree and obtains a value of a neighbor pattern. The neighbor node pattern is used to infer the occupancy pattern of the node. The up part of FIG. 7 shows a cube corresponding to a node (a cube positioned in the middle) and six cubes (neighbor nodes) sharing at least one face with the cube. The nodes shown in the figure are nodes of the same depth. The numbers shown in the figure represent weights (1, 2, 4, 8, 16, and 32) associated with the six nodes, respectively. The weights are assigned sequentially according to the positions of neighboring nodes.

The down part of FIG. 7 shows neighbor node pattern values. A neighbor node pattern value is the sum of values multiplied by the weight of an occupied neighbor node (a neighbor node having a point). Accordingly, the neighbor node pattern values are 0 to 63. When the neighbor node pattern value is 0, it indicates that there is no node having a point (no occupied node) among the neighbor nodes of the node. When the neighbor node pattern value is 63, it indicates that all neighbor nodes are occupied nodes. As shown in the figure, since neighbor nodes to which weights 1, 2, 4, and 8 are assigned are occupied nodes, the neighbor node pattern value is 15, the sum of 1, 2, 4, and 8. The point cloud video encoder may perform coding according to the neighbor node pattern value (for example, when the neighbor node pattern value is 63, 64 kinds of coding may be performed). According to embodiments, the point cloud video encoder may reduce coding complexity by changing a neighbor node pattern value (for example, based on a table by which 64 is changed to 10 or 6).

FIG. 8 illustrates an example of point configuration in each LOD according to embodiments.

As described with reference to FIGS. 1 to 7 , encoded geometry is reconstructed (decompressed) before attribute encoding is performed. When direct coding is applied, the geometry reconstruction operation may include changing the placement of direct coded points (e.g., placing the direct coded points in front of the point cloud data). When trisoup geometry encoding is applied, the geometry reconstruction process is performed through triangle reconstruction, up-sampling, and voxelization. Since the attribute depends on the geometry, attribute encoding is performed based on the reconstructed geometry.

The point cloud video encoder (for example, the LOD generator 40009) may classify (reorganize or group) points by LOD. FIG. 8 shows the point cloud content corresponding to LODs. The leftmost picture in FIG. 8 represents original point cloud content. The second picture from the left of FIG. 8 represents distribution of the points in the lowest LOD, and the rightmost picture in FIG. 8 represents distribution of the points in the highest LOD. That is, the points in the lowest LOD are sparsely distributed, and the points in the highest LOD are densely distributed. That is, as the LOD rises in the direction pointed by the arrow indicated at the bottom of FIG. 8 , the space (or distance) between points is narrowed.

FIG. 9 illustrates an example of point configuration for each LOD according to embodiments.

As described with reference to FIGS. 1 to 8 , the point cloud content providing system, or the point cloud video encoder (for example, the point cloud video encoder 10002 of FIG. 1 , the point cloud video encoder of FIG. 4 , or the LOD generator 40009) may generates an LOD. The LOD is generated by reorganizing the points into a set of refinement levels according to a set LOD distance value (or a set of Euclidean distances). The LOD generation process is performed not only by the point cloud video encoder, but also by the point cloud video decoder.

The upper part of FIG. 9 shows examples (P0 to P9) of points of the point cloud content distributed in a 3D space. In FIG. 9 , the original order represents the order of points P0 to P9 before LOD generation. In FIG. 9 , the LOD based order represents the order of points according to the LOD generation. Points are reorganized by LOD. Also, a high LOD contains the points belonging to lower LODs. As shown in FIG. 9 , LOD0 contains P0, P5, P4 and P2. LOD1 contains the points of LOD0, P1, P6 and P3. LOD2 contains the points of LOD0, the points of LOD1, P9, P8 and P7.

As described with reference to FIG. 4 , the point cloud video encoder according to the embodiments may perform prediction transform coding based on LOD, lifting transform coding based on LOD, and RAHT transform coding selectively or in combination.

The point cloud video encoder according to the embodiments may generate a predictor for points to perform prediction transform coding based on LOD for setting a predicted attribute (or predicted attribute value) of each point. That is, N predictors may be generated for N points. The predictor according to the embodiments may calculate a weight (=1/distance) based on the LOD value of each point, indexing information about neighboring points present within a set distance for each LOD, and a distance to the neighboring points.

The predicted attribute (or attribute value) according to the embodiments is set to the average of values obtained by multiplying the attributes (or attribute values) (e.g., color, reflectance, etc.) of neighbor points set in the predictor of each point by a weight (or weight value) calculated based on the distance to each neighbor point. The point cloud video encoder according to the embodiments (for example, the coefficient quantizer 40011) may quantize and inversely quantize the residual of each point (which may be called residual attribute, residual attribute value, attribute prediction residual value or prediction error attribute value and so on) obtained by subtracting a predicted attribute (or attribute value) each point from the attribute (i.e., original attribute value) of each point. The quantization process performed for a residual attribute value in a transmission device is configured as shown in table 2. The inverse quantization process performed for a residual attribute value in a reception device is configured as shown in table 3.

TABLE 2 int PCCQuantization(int value, int quantStep) { if( value >=0) { return floor(value / quantStep + 1.0 / 3.0); } else { return −floor(−value / quantStep + 1.0 / 3.0); } }

TABLE 3 int PCCInverseQuantization(int value, int quantStep) { if( quantStep ==0) { return value; } else { return value * quantStep; } }

When the predictor of each point has neighbor points, the point cloud video encoder (e.g., the arithmetic encoder 40012) according to the embodiments may perform entropy coding on the quantized and inversely quantized residual attribute values as described above. When the predictor of each point has no neighbor point, the point cloud video encoder according to the embodiments (for example, the arithmetic encoder 40012) may perform entropy coding on the attributes of the corresponding point without performing the above-described operation.

The point cloud video encoder according to the embodiments (for example, the lifting transformer 40010) may generate a predictor of each point, set the calculated LOD and register neighbor points in the predictor, and set weights according to the distances to neighbor points to perform lifting transform coding. The lifting transform coding according to the embodiments is similar to the above-described prediction transform coding, but differs therefrom in that weights are cumulatively applied to attribute values. The process of cumulatively applying weights to the attribute values according to embodiments is configured as follows.

1) Create an array Quantization Weight (QW) for storing the weight value of each point. The initial value of all elements of QW is 1.0. Multiply the QW values of the predictor indexes of the neighbor nodes registered in the predictor by the weight of the predictor of the current point, and add the values obtained by the multiplication.

2) Lift prediction process: Subtract the value obtained by multiplying the attribute value of the point by the weight from the existing attribute value to calculate a predicted attribute value.

3) Create temporary arrays called updateweight and update and initialize the temporary arrays to zero.

4) Cumulatively add the weights calculated by multiplying the weights calculated for all predictors by a weight stored in the QW corresponding to a predictor index to the updateweight array as indexes of neighbor nodes. Cumulatively add, to the update array, a value obtained by multiplying the attribute value of the index of a neighbor node by the calculated weight.

5) Lift update process: Divide the attribute values of the update array for all predictors by the weight value of the updateweight array of the predictor index, and add the existing attribute value to the values obtained by the division.

6) Calculate predicted attributes by multiplying the attribute values updated through the lift update process by the weight updated through the lift prediction process (stored in the QW) for all predictors. The point cloud video encoder (e.g., coefficient quantizer 40011) according to the embodiments quantizes the predicted attribute values. In addition, the point cloud video encoder (e.g., the arithmetic encoder 40012) performs entropy coding on the quantized attribute values.

The point cloud video encoder (for example, the RAHT transformer 40008) according to the embodiments may perform RAHT transform coding in which attributes of nodes of a higher level are predicted using the attributes associated with nodes of a lower level in the octree. RAHT transform coding is an example of attribute intra coding through an octree backward scan. The point cloud video encoder according to the embodiments scans the entire region from the voxel and repeats the merging process of merging the voxels into a larger block at each step until the root node is reached. The merging process according to the embodiments is performed only on the occupied nodes. The merging process is not performed on the empty node. The merging process is performed on an upper node immediately above the empty node.

Equation 3 below represents a RAHT transformation matrix. In Equation 3, g_(l) _(x,y,z) denotes the average attribute value of voxels at level l. g_(l) _(x,y,z) may be calculated based on g_(l+1) _(2x,y,z) and g_(l+1) _(2x+1,y,z) . The weights for g_(l) _(2x,y,z) and g_(l) _(2x+1,y,z) are w1=w_(l) _(2x,y,z) and w2=w_(l) _(2x+1,y,z) .

$\begin{matrix} {{\begin{bmatrix} g_{l - 1_{x,y,z}} \\ h_{l - 1_{x,y,z}} \end{bmatrix} = {T_{w\; 1w\; 2}\begin{bmatrix} g_{l_{{2x},y,z}} \\ g_{l_{{{2x} + 1},y,z}} \end{bmatrix}}}{T_{w1w2} = {\frac{1}{\sqrt{{w1} + {w2}}}\begin{bmatrix} \sqrt{w1} & \sqrt{w2} \\ {- \sqrt{w2}} & \sqrt{w1} \end{bmatrix}}}} & {{Equation}\mspace{14mu} 3} \end{matrix}$

Here, g_(l−1) _(x,y,z) is a low-pass value and is used in the merging process at the next higher level. h_(l−1) _(x,y,z) denotes high-pass coefficients. The high-pass coefficients at each step are quantized and subjected to entropy coding (for example, encoding by the arithmetic encoder 40012). The weights are calculated as w_(l) _(−1 x,y,z) =w_(l) _(2x+1,y,z) . The root node is created through the g₁ _(0,0,0) and g₁ _(0,0,1) as Equation 4.

$\begin{matrix} {\left\lceil \begin{matrix} {gDC} \\ h_{0_{0,0,0}} \end{matrix} \right\rceil = {T_{w\; 1000\; w\; 1001}\left\lceil \begin{matrix} g_{1_{0,0,{0z}}} \\ g_{1_{0,0,1}} \end{matrix} \right\rceil}} & {{Equation}\mspace{14mu} 4} \end{matrix}$

The value of gDC is also quantized and subjected to entropy coding like the high-pass coefficients.

FIG. 10 illustrates a point cloud video decoder according to embodiments.

The point cloud video decoder illustrated in FIG. 10 is an example of the point cloud video decoder 10006 described in FIG. 1 , and may perform the same or similar operations as the operations of the point cloud video decoder 10006 illustrated in FIG. 1 . As shown in the figure, the point cloud video decoder may receive a geometry bitstream and an attribute bitstream contained in one or more bitstreams. The point cloud video decoder includes a geometry decoder and an attribute decoder. The geometry decoder performs geometry decoding on the geometry bitstream and outputs decoded geometry. The attribute decoder performs attribute decoding on the attribute bitstream based on the decoded geometry, and outputs decoded attributes. The decoded geometry and decoded attributes are used to reconstruct point cloud content (a decoded point cloud).

FIG. 11 illustrates a point cloud video decoder according to embodiments.

The point cloud video decoder illustrated in FIG. 11 is an example of the point cloud video decoder illustrated in FIG. 10 , and may perform a decoding operation, which is an inverse process of the encoding operation of the point cloud video encoder illustrated in FIGS. 1 to 9 .

As described with reference to FIGS. 1 and 10 , the point cloud video decoder may perform geometry decoding and attribute decoding. The geometry decoding is performed before the attribute decoding.

The point cloud video decoder according to the embodiments includes an arithmetic decoder (Arithmetic decode) 11000, an octree synthesizer (Synthesize octree) 11001, a surface approximation synthesizer (Synthesize surface approximation) 11002, and a geometry reconstructor (Reconstruct geometry) 11003, a coordinate inverse transformer (Inverse transform coordinates) 11004, an arithmetic decoder (Arithmetic decode) 11005, an inverse quantizer (Inverse quantize) 11006, a RAHT transformer 11007, an LOD generator (Generate LOD) 11008, an inverse lifter (inverse lifting) 11009, and/or a color inverse transformer (Inverse transform colors) 11010.

The arithmetic decoder 11000, the octree synthesizer 11001, the surface approximation synthesizer 11002, and the geometry reconstructor 11003, and the coordinate inverse transformer 11004 may perform geometry decoding. The geometry decoding according to the embodiments may include direct decoding and trisoup geometry decoding. The direct decoding and trisoup geometry decoding are selectively applied. The geometry decoding is not limited to the above-described example, and is performed as an inverse process of the geometry encoding described with reference to FIGS. 1 to 9 .

The arithmetic decoder 11000 according to the embodiments decodes the received geometry bitstream based on the arithmetic coding. The operation of the arithmetic decoder 11000 corresponds to the inverse process of the arithmetic encoder 40004.

The octree synthesizer 11001 according to the embodiments may generate an octree by acquiring an occupancy code from the decoded geometry bitstream (or information on the geometry secured as a result of decoding). The occupancy code is configured as described in detail with reference to FIGS. 1 to 9 .

When the trisoup geometry encoding is applied, the surface approximation synthesizer 11002 according to the embodiments may synthesize a surface based on the decoded geometry and/or the generated octree.

The geometry reconstructor 11003 according to the embodiments may regenerate geometry based on the surface and/or the decoded geometry. As described with reference to FIGS. 1 to 9 , direct coding and trisoup geometry encoding are selectively applied. Accordingly, the geometry reconstructor 11003 directly imports and adds position information about the points to which direct coding is applied. When the trisoup geometry encoding is applied, the geometry reconstructor 11003 may reconstruct the geometry by performing the reconstruction operations of the geometry reconstructor 40005, for example, triangle reconstruction, up-sampling, and voxelization. Details are the same as those described with reference to FIG. 6 , and thus description thereof is omitted. The reconstructed geometry may include a point cloud picture or frame that does not contain attributes.

The coordinate inverse transformer 11004 according to the embodiments may acquire positions of the points by transforming the coordinates based on the reconstructed geometry.

The arithmetic decoder 11005, the inverse quantizer 11006, the RAHT transformer 11007, the LOD generator 11008, the inverse lifter 11009, and/or the color inverse transformer 11010 may perform the attribute decoding described with reference to FIG. 10 . The attribute decoding according to the embodiments includes region adaptive hierarchical transform (RAHT) decoding, interpolation-based hierarchical nearest-neighbor prediction (prediction transform) decoding, and interpolation-based hierarchical nearest-neighbor prediction with an update/lifting step (lifting transform) decoding. The three decoding schemes described above may be used selectively, or a combination of one or more decoding schemes may be used. The attribute decoding according to the embodiments is not limited to the above-described example.

The arithmetic decoder 11005 according to the embodiments decodes the attribute bitstream by arithmetic coding.

The inverse quantizer 11006 according to the embodiments inversely quantizes the information about the decoded attribute bitstream or attributes secured as a result of the decoding, and outputs the inversely quantized attributes (or attribute values). The inverse quantization may be selectively applied based on the attribute encoding of the point cloud video encoder.

According to embodiments, the RAHT transformer 11007, the LOD generator 11008, and/or the inverse lifter 11009 may process the reconstructed geometry and the inversely quantized attributes. As described above, the RAHT transformer 11007, the LOD generator 11008, and/or the inverse lifter 11009 may selectively perform a decoding operation corresponding to the encoding of the point cloud video encoder.

The color inverse transformer 11010 according to the embodiments performs inverse transform coding to inversely transform a color value (or texture) included in the decoded attributes. The operation of the color inverse transformer 11010 may be selectively performed based on the operation of the color transformer 40006 of the point cloud video encoder.

Although not shown in the figure, the elements of the point cloud video decoder of FIG. 11 may be implemented by hardware including one or more processors or integrated circuits configured to communicate with one or more memories included in the point cloud content providing apparatus, software, firmware, or a combination thereof. The one or more processors may perform at least one or more of the operations and/or functions of the elements of the point cloud video decoder of FIG. 11 described above. Additionally, the one or more processors may operate or execute a set of software programs and/or instructions for performing the operations and/or functions of the elements of the point cloud video decoder of FIG. 11 .

FIG. 12 illustrates a transmission device according to embodiments.

The transmission device shown in FIG. 12 is an example of the transmission device 10000 of FIG. 1 (or the point cloud video encoder of FIG. 4 ). The transmission device illustrated in FIG. 12 may perform one or more of the operations and methods the same as or similar to those of the point cloud video encoder described with reference to FIGS. 1 to 9 . The transmission device according to the embodiments may include a data input unit 12000, a quantization processor 12001, a voxelization processor 12002, an octree occupancy code generator 12003, a surface model processor 12004, an intra/inter-coding processor 12005, an arithmetic coder 12006, a metadata processor 12007, a color transform processor 12008, an attribute transform processor 12009, a prediction/lifting/RAHT transform processor 12010, an arithmetic coder 12011 and/or a transmission processor 12012.

The data input unit 12000 according to the embodiments receives or acquires point cloud data. The data input unit 12000 may perform an operation and/or acquisition method the same as or similar to the operation and/or acquisition method of the point cloud video acquisition unit 10001 (or the acquisition process 20000 described with reference to FIG. 2 ).

The data input unit 12000, the quantization processor 12001, the voxelization processor 12002, the octree occupancy code generator 12003, the surface model processor 12004, the intra/inter-coding processor 12005, and the arithmetic coder 12006 perform geometry encoding. The geometry encoding according to the embodiments is the same as or similar to the geometry encoding described with reference to FIGS. 1 to 9 , and thus a detailed description thereof is omitted.

The quantization processor 12001 according to the embodiments quantizes geometry (e.g., position values of points). The operation and/or quantization of the quantization processor 12001 is the same as or similar to the operation and/or quantization of the quantizer 40001 described with reference to FIG. 4 . Details are the same as those described with reference to FIGS. 1 to 9 .

The voxelization processor 12002 according to embodiments voxelizes the quantized position values of the points. The voxelization processor 12002 may perform an operation and/or process the same or similar to the operation and/or the voxelization process of the quantizer 40001 described with reference to FIG. 4 . Details are the same as those described with reference to FIGS. 1 to 9 .

The octree occupancy code generator 12003 according to the embodiments performs octree coding on the voxelized positions of the points based on an octree structure. The octree occupancy code generator 12003 may generate an occupancy code. The octree occupancy code generator 12003 may perform an operation and/or method the same as or similar to the operation and/or method of the point cloud video encoder (or the octree analyzer 40002) described with reference to FIGS. 4 and 6 . Details are the same as those described with reference to FIGS. 1 to 9 .

The surface model processor 12004 according to the embodiments may perform trisoup geometry encoding based on a surface model to reconstruct the positions of points in a specific region (or node) on a voxel basis. The surface model processor 12004 may perform an operation and/or method the same as or similar to the operation and/or method of the point cloud video encoder (for example, the surface approximation analyzer 40003) described with reference to FIG. 4 . Details are the same as those described with reference to FIGS. 1 to 9 .

The intra/inter-coding processor 12005 according to the embodiments may perform intra/inter-coding on point cloud data. The intra/inter-coding processor 12005 may perform coding the same as or similar to the intra/inter-coding described with reference to FIG. 7 . Details are the same as those described with reference to FIG. 7 . According to embodiments, the intra/inter-coding processor 12005 may be included in the arithmetic coder 12006.

The arithmetic coder 12006 according to the embodiments performs entropy encoding on an octree of the point cloud data and/or an approximated octree. For example, the encoding scheme includes arithmetic encoding. The arithmetic coder 12006 performs an operation and/or method the same as or similar to the operation and/or method of the arithmetic encoder 40004.

The metadata processor 12007 according to the embodiments processes metadata about the point cloud data, for example, a set value, and provides the same to a necessary processing process such as geometry encoding and/or attribute encoding. Also, the metadata processor 12007 according to the embodiments may generate and/or process signaling information related to the geometry encoding and/or the attribute encoding. The signaling information according to the embodiments may be encoded separately from the geometry encoding and/or the attribute encoding. The signaling information according to the embodiments may be interleaved.

The color transform processor 12008, the attribute transform processor 12009, the prediction/lifting/RAHT transform processor 12010, and the arithmetic coder 12011 perform the attribute encoding. The attribute encoding according to the embodiments is the same as or similar to the attribute encoding described with reference to FIGS. 1 to 9 , and thus a detailed description thereof is omitted.

The color transform processor 12008 according to the embodiments performs color transform coding to transform color values included in attributes. The color transform processor 12008 may perform color transform coding based on the reconstructed geometry. The reconstructed geometry is the same as described with reference to FIGS. 1 to 9 . Also, it performs an operation and/or method the same as or similar to the operation and/or method of the color transformer 40006 described with reference to FIG. 4 is performed. The detailed description thereof is omitted.

The attribute transform processor 12009 according to the embodiments performs attribute transformation to transform the attributes based on the reconstructed geometry and/or the positions on which geometry encoding is not performed. The attribute transform processor 12009 performs an operation and/or method the same as or similar to the operation and/or method of the attribute transformer 40007 described with reference to FIG. 4 . The detailed description thereof is omitted. The prediction/lifting/RAHT transform processor 12010 according to the embodiments may code the transformed attributes by any one or a combination of RAHT coding, prediction transform coding, and lifting transform coding. The prediction/lifting/RAHT transform processor 12010 performs at least one of the operations the same as or similar to the operations of the RAHT transformer 40008, the LOD generator 40009, and the lifting transformer 40010 described with reference to FIG. 4 . In addition, the prediction transform coding, the lifting transform coding, and the RAHT transform coding are the same as those described with reference to FIGS. 1 to 9 , and thus a detailed description thereof is omitted.

The arithmetic coder 12011 according to the embodiments may encode the coded attributes based on the arithmetic coding. The arithmetic coder 12011 performs an operation and/or method the same as or similar to the operation and/or method of the arithmetic encoder 40012.

The transmission processor 12012 according to the embodiments may transmit each bitstream containing encoded geometry and/or encoded attributes and metadata, or transmit one bitstream configured with the encoded geometry and/or the encoded attributes and the metadata. When the encoded geometry and/or the encoded attributes and the metadata according to the embodiments are configured into one bitstream, the bitstream may include one or more sub-bitstreams. The bitstream according to the embodiments may contain signaling information including a sequence parameter set (SPS) for signaling of a sequence level, a geometry parameter set (GPS) for signaling of geometry information coding, an attribute parameter set (APS) for signaling of attribute information coding, and a tile parameter set (TPS or tile inventory) for signaling of a tile level, and slice data. The slice data may include information about one or more slices. One slice according to embodiments may include one geometry bitstream Geom0⁰ and one or more attribute bitstreams Attr0⁰ and Attr1⁰.

The slice is a series of a syntax element representing in whole or in part of the coded point cloud frame.

The TPS according to the embodiments may include information about each tile (for example, coordinate information and height/size information about a bounding box) for one or more tiles. The geometry bitstream may contain a header and a payload. The header of the geometry bitstream according to the embodiments may contain a parameter set identifier (geom_parameter_set_id), a tile identifier (geom_tile_id) and a slice identifier (geom_slice_id) included in the GPS, and information about the data contained in the payload. As described above, the metadata processor 12007 according to the embodiments may generate and/or process the signaling information and transmit the same to the transmission processor 12012. According to embodiments, the elements to perform geometry encoding and the elements to perform attribute encoding may share data/information with each other as indicated by dotted lines. The transmission processor 12012 according to the embodiments may perform an operation and/or transmission method the same as or similar to the operation and/or transmission method of the transmitter 10003. Details are the same as those described with reference to FIGS. 1 and 2 , and thus a description thereof is omitted.

FIG. 13 illustrates a reception device according to embodiments.

The reception device illustrated in FIG. 13 is an example of the reception device 10004 of FIG. 1 (or the point cloud video decoder of FIGS. 10 and 11 ). The reception device illustrated in FIG. 13 may perform one or more of the operations and methods the same as or similar to those of the point cloud video decoder described with reference to FIGS. 1 to 11 .

The reception device according to the embodiment includes a receiver 13000, a reception processor 13001, an arithmetic decoder 13002, an occupancy code-based octree reconstruction processor 13003, a surface model processor (triangle reconstruction, up-sampling, voxelization) 13004, an inverse quantization processor 13005, a metadata parser 13006, an arithmetic decoder 13007, an inverse quantization processor 13008, a prediction/lifting/RAHT inverse transform processor 13009, a color inverse transform processor 13010, and/or a renderer 13011. Each element for decoding according to the embodiments may perform an inverse process of the operation of a corresponding element for encoding according to the embodiments.

The receiver 13000 according to the embodiments receives point cloud data. The receiver 13000 may perform an operation and/or reception method the same as or similar to the operation and/or reception method of the receiver 10005 of FIG. 1 . The detailed description thereof is omitted.

The reception processor 13001 according to the embodiments may acquire a geometry bitstream and/or an attribute bitstream from the received data. The reception processor 13001 may be included in the receiver 13000.

The arithmetic decoder 13002, the occupancy code-based octree reconstruction processor 13003, the surface model processor 13004, and the inverse quantization processor 1305 may perform geometry decoding. The geometry decoding according to embodiments is the same as or similar to the geometry decoding described with reference to FIGS. 1 to 10 , and thus a detailed description thereof is omitted.

The arithmetic decoder 13002 according to the embodiments may decode the geometry bitstream based on arithmetic coding. The arithmetic decoder 13002 performs an operation and/or coding the same as or similar to the operation and/or coding of the arithmetic decoder 11000.

The occupancy code-based octree reconstruction processor 13003 according to the embodiments may reconstruct an octree by acquiring an occupancy code from the decoded geometry bitstream (or information about the geometry secured as a result of decoding). The occupancy code-based octree reconstruction processor 13003 performs an operation and/or method the same as or similar to the operation and/or octree generation method of the octree synthesizer 11001. When the trisoup geometry encoding is applied, the surface model processor 1302 according to the embodiments may perform trisoup geometry decoding and related geometry reconstruction (for example, triangle reconstruction, up-sampling, voxelization) based on the surface model method. The surface model processor 1302 performs an operation the same as or similar to that of the surface approximation synthesizer 11002 and/or the geometry reconstructor 11003.

The inverse quantization processor 1305 according to the embodiments may inversely quantize the decoded geometry.

The metadata parser 1306 according to the embodiments may parse metadata contained in the received point cloud data, for example, a set value. The metadata parser 1306 may pass the metadata to geometry decoding and/or attribute decoding. The metadata is the same as that described with reference to FIG. 12 , and thus a detailed description thereof is omitted.

The arithmetic decoder 13007, the inverse quantization processor 13008, the prediction/lifting/RAHT inverse transform processor 13009 and the color inverse transform processor 13010 perform attribute decoding. The attribute decoding is the same as or similar to the attribute decoding described with reference to FIGS. 1 to 10 , and thus a detailed description thereof is omitted.

The arithmetic decoder 13007 according to the embodiments may decode the attribute bitstream by arithmetic coding. The arithmetic decoder 13007 may decode the attribute bitstream based on the reconstructed geometry. The arithmetic decoder 13007 performs an operation and/or coding the same as or similar to the operation and/or coding of the arithmetic decoder 11005.

The inverse quantization processor 13008 according to the embodiments may inversely quantize the decoded attribute bitstream. The inverse quantization processor 13008 performs an operation and/or method the same as or similar to the operation and/or inverse quantization method of the inverse quantizer 11006.

The prediction/lifting/RAHT inverse transformer 13009 according to the embodiments may process the reconstructed geometry and the inversely quantized attributes. The prediction/lifting/RAHT inverse transform processor 1301 performs one or more of operations and/or decoding the same as or similar to the operations and/or decoding of the RAHT transformer 11007, the LOD generator 11008, and/or the inverse lifter 11009. The color inverse transform processor 13010 according to the embodiments performs inverse transform coding to inversely transform color values (or textures) included in the decoded attributes. The color inverse transform processor 13010 performs an operation and/or inverse transform coding the same as or similar to the operation and/or inverse transform coding of the color inverse transformer 11010. The renderer 13011 according to the embodiments may render the point cloud data.

FIG. 14 shows an exemplary structure operatively connectable with a method/device for transmitting and receiving point cloud data according to embodiments.

The structure of FIG. 14 represents a configuration in which at least one of a server 17600, a robot 17100, a self-driving vehicle 17200, an XR device 17300, a smartphone 17400, a home appliance 17500, and/or a head-mount display (HMD) 17700 is connected to a cloud network 17100. The robot 17100, the self-driving vehicle 17200, the XR device 17300, the smartphone 17400, or the home appliance 17500 is referred to as a device. In addition, the XR device 17300 may correspond to a point cloud compressed data (PCC) device according to embodiments or may be operatively connected to the PCC device.

The cloud network 17000 may represent a network that constitutes part of the cloud computing infrastructure or is present in the cloud computing infrastructure. Here, the cloud network 17000 may be configured using a 3G network, 4G or Long Term Evolution (LTE) network, or a 5G network.

The server 17600 may be connected to at least one of the robot 17100, the self-driving vehicle 17200, the XR device 17300, the smartphone 17400, the home appliance 17500, and/or the HMD 17700 over the cloud network 17000 and may assist in at least a part of the processing of the connected devices 17100 to 17700.

The HMD 17700 represents one of the implementation types of the XR device and/or the PCC device according to the embodiments. The HMD type device according to the embodiments includes a communication unit, a control unit, a memory, an I/O unit, a sensor unit, and a power supply unit.

Hereinafter, various embodiments of the devices 17100 to 17500 to which the above-described technology is applied will be described. The devices 17100 to 17500 illustrated in FIG. 14 may be operatively connected/coupled to a point cloud data transmission device and reception according to the above-described embodiments.

<PCC+XR>

The XR/PCC device 17300 may employ PCC technology and/or XR (AR+VR) technology, and may be implemented as an HMD, a head-up display (HUD) provided in a vehicle, a television, a mobile phone, a smartphone, a computer, a wearable device, a home appliance, a digital signage, a vehicle, a stationary robot, or a mobile robot.

The XR/PCC device 17300 may analyze 3D point cloud data or image data acquired through various sensors or from an external device and generate position data and attribute data about 3D points. Thereby, the XR/PCC device 17300 may acquire information about the surrounding space or a real object, and render and output an XR object. For example, the XR/PCC device 17300 may match an XR object including auxiliary information about a recognized object with the recognized object and output the matched XR object.

<PCC+Self-Driving+XR>

The self-driving vehicle 17200 may be implemented as a mobile robot, a vehicle, an unmanned aerial vehicle, or the like by applying the PCC technology and the XR technology.

The self-driving vehicle 17200 to which the XR/PCC technology is applied may represent a self-driving vehicle provided with means for providing an XR image, or a self-driving vehicle that is a target of control/interaction in the XR image. In particular, the self-driving vehicle 17200 which is a target of control/interaction in the XR image may be distinguished from the XR device 17300 and may be operatively connected thereto.

The self-driving vehicle 17200 having means for providing an XR/PCC image may acquire sensor information from sensors including a camera, and output the generated XR/PCC image based on the acquired sensor information. For example, the self-driving vehicle 17200 may have an HUD and output an XR/PCC image thereto, thereby providing an occupant with an XR/PCC object corresponding to a real object or an object present on the screen.

When the XR/PCC object is output to the HUD, at least a part of the XR/PCC object may be output to overlap the real object to which the occupant's eyes are directed. On the other hand, when the XR/PCC object is output on a display provided inside the self-driving vehicle, at least a part of the XR/PCC object may be output to overlap an object on the screen. For example, the self-driving vehicle 17200 may output XR/PCC objects corresponding to objects such as a road, another vehicle, a traffic light, a traffic sign, a two-wheeled vehicle, a pedestrian, and a building.

The virtual reality (VR) technology, the augmented reality (AR) technology, the mixed reality (MR) technology and/or the point cloud compression (PCC) technology according to the embodiments are applicable to various devices.

In other words, the VR technology is a display technology that provides only CG images of real-world objects, backgrounds, and the like. On the other hand, the AR technology refers to a technology that shows a virtually created CG image on the image of a real object. The MR technology is similar to the AR technology described above in that virtual objects to be shown are mixed and combined with the real world. However, the MR technology differs from the AR technology in that the AR technology makes a clear distinction between a real object and a virtual object created as a CG image and uses virtual objects as complementary objects for real objects, whereas the MR technology treats virtual objects as objects having equivalent characteristics as real objects. More specifically, an example of MR technology applications is a hologram service.

Recently, the VR, AR, and MR technologies are sometimes referred to as extended reality (XR) technology rather than being clearly distinguished from each other. Accordingly, embodiments of the present disclosure are applicable to any of the VR, AR, MR, and XR technologies. The encoding/decoding based on PCC, V-PCC, and G-PCC techniques is applicable to such technologies.

The PCC method/device according to the embodiments may be applied to a vehicle that provides a self-driving service.

A vehicle that provides the self-driving service is connected to a PCC device for wired/wireless communication.

When the point cloud compression data (PCC) transmission/reception device according to the embodiments is connected to a vehicle for wired/wireless communication, the device may receive/process content data related to an AR/VR/PCC service, which may be provided together with the self-driving service, and transmit the same to the vehicle. In the case where the PCC transmission/reception device is mounted on a vehicle, the PCC transmission/reception device may receive/process content data related to the AR/VR/PCC service according to a user input signal input through a user interface device and provide the same to the user. The vehicle or the user interface device according to the embodiments may receive a user input signal. The user input signal according to the embodiments may include a signal indicating the self-driving service.

Meanwhile, the point cloud video encoder on the transmitting side may further perform a spatial partitioning process of spatially partitioning (or dividing) the point cloud data into one or more 3D blocks before encoding the point cloud data. That is, in order for the encoding and transmission operations of the transmission device and the decoding and rendering operations of the reception device to be performed in real time and processed with low latency, the transmission device may spatially partition the point cloud data into a plurality of regions. In addition, the transmission device may independently or non-independently encode the spatially partitioned regions (or blocks), thereby enabling random access and parallel encoding in the three-dimensional space occupied by the point cloud data. In addition, the transmission device and the reception device may perform encoding and decoding independently or non-independently for each spatially partitioned region (or block), thereby preventing errors from being accumulated in the encoding and decoding process.

FIG. 15 is a diagram illustrating another example of a point cloud transmission device according to embodiments, including a spatial partitioner.

The point cloud transmission device according to the embodiments may include a data input unit 51001, a coordinates transformation unit 51002, a quantization processor 51003, a spatial partitioner 51004, a signaling processor 51005, a geometry encoder 51006, an attribute encoder 51007, and a transmission processor 51008. According to embodiments, the coordinates transformation unit 51002, the quantization processor 51003, the spatial partitioner 51004, the geometry encoder 51006, and the attribute encoder 51007 may be referred to as point cloud video encoders.

The data input unit 51001 may perform some or all of the operations of the point cloud video acquisition unit 10001 of FIG. 1 , or may perform some or all of the operations of the data input unit 12000 of FIG. 12 . The coordinates transformation unit 51002 may perform some or all of the operations of the coordinates transformation unit 40000 of FIG. 4 . Further, the quantization processor 51003 may perform some or all of the operations of the quantization unit 40001 of FIG. 4 , or may perform some or all of the operations of the quantization processor 12001 of FIG. 12 .

The spatial partitioner 51004 may spatially partition the point cloud data quantized and output from the quantization processor 51003 into one or more 3D blocks based on a bounding box and/or a sub-bounding box. Here, the 3D block may refer to a tile group, a tile, a slice, a coding unit (CU), a prediction unit (PU), or a transform unit (TU). In one embodiment, the signaling information for spatial partition is entropy-encoded by the signaling processor 51005 and then transmitted through the transmission processor 51008 in the form of a bitstream.

FIGS. 16A to 16C illustrate an embodiment of partitioning a bounding box into one or more tiles. As shown in FIG. 16A, a point cloud object, which corresponds to point cloud data, may be expressed in the form of a box based on a coordinate system, which is referred to as a bounding box. In other words, the bounding box represents a cube capable of containing all points of the point cloud.

FIG. 16B and FIG. 16C illustrate an example in which the bounding box of FIG. 16A is partitioned into tile 1 # and tile 2 #, and tile 2 # is partitioned again into slice 1 # and slice 2 #.

In one embodiment, the point cloud content may be one person such as an actor, multiple people, one object, or multiple objects. In a larger range, it may be a map for autonomous driving or a map for indoor navigation of a robot. In this case, the point cloud content may be a vast amount of locally connected data. In this case, the point cloud content cannot be encoded/decoded at once, and accordingly tile partitioning may be performed before the point cloud content is compressed. For example, room #101 in a building may be partitioned into one tile and room #102 in the building may be partitioned into another tile. In order to support fast encoding/decoding by applying parallelization to the partitioned tiles, the tiles may be partitioned (or split) into slices again. This operation may be referred to as slice partitioning (or splitting).

That is, a tile may represent a partial region (e.g., a rectangular cube) of a 3D space occupied by point cloud data according to embodiments. According to embodiments, a tile may include one or more slices. The tile according to the embodiments may be partitioned into one or more slices, and thus the point cloud video encoder may encode point cloud data in parallel.

A slice may represent a unit of data (or bitstream) that may be independently encoded by the point cloud video encoder according to the embodiments and/or a unit of data (or bitstream) that may be independently decoded by the point cloud video decoder. A slice may be a set of data in a 3D space occupied by point cloud data, or a set of some data among the point cloud data. A slice according to the embodiments may represent a region or set of points included in a tile according to embodiments. According to embodiments, a tile may be partitioned into one or more slices based on the number of points included in one tile. For example, one tile may be a set of points partitioned by the number of points. According to embodiments, a tile may be partitioned into one or more slices based on the number of points, and some data may be split or merged in the partitioning process. That is, a slice may be a unit that may be independently coded within a corresponding tile. In this way, a tile obtained by spatially partitioning may be partitioned into one or more slices for fast and efficient processing.

The point cloud video encoder according to the embodiments may encode point cloud data on a slice-by-slice basis or a tile-by-tile basis, wherein a tile includes one or more slices. In addition, the point cloud video encoder according to the embodiments may perform different quantization and/or transformation for each tile or each slice.

Positions of one or more 3D blocks (e.g., slices) spatially partitioned by the spatial partitioner 51004 are output to the geometry encoder 51006, and the attribute information (or attributes) is output to the attribute encoder 51007. The positions may be position information about the points included in a partitioned unit (box, block, tile, tile group, or slice), and are referred to as geometry information.

The geometry encoder 51006 constructs and encodes (i.e., compresses) an octree based on the positions output from the spatial partitioner 51004 to output a geometry bitstream. The geometry encoder 51006 may reconstruct an octree and/or an approximated octree and output the same to the attribute encoder 51007. The reconstructed octree may be referred to as reconstructed geometry (or restored geometry).

The attribute encoder 51007 encodes (i.e., compresses) the attributes output from the spatial partitioner 51004 based on the reconstructed geometry output from the geometry encoder 51006, and outputs an attribute bitstream.

FIG. 17 is a detailed block diagram illustrating another example of the geometry encoder 51006 and the attribute encoder 51007 according to embodiments.

The voxelization processor 53001, the octree generator 53002, the geometry information predictor 53003, and the arithmetic coder 53004 of the geometry encoder 51006 of FIG. 17 may perform some or all of the operations of the octree analysis unit 40002, the surface approximation analysis unit 40003, the arithmetic encoder 40004, and the geometry reconstruction unit 40005 of FIG. 4 , or may perform some or all of the operations of the voxelization processor 12002, the octree occupancy code generator 12003, and the surface model processor 12004, the intra/inter-coding processor 12005, and the arithmetic coder 12006 of FIG.

The attribute encoder 51007 of FIG. 17 may include a color transformation processor 53005, an attribute transformation processor 5306, a LOD configuration unit 53007, a neighbor point group configuration unit 53008, an attribute information prediction unit 53009, a residual attribute information quantization processor 53010, and an arithmetic coder 53011.

In an embodiment, a quantization processor may be further provided between the spatial partitioner 51004 and the voxelization processor 53001. The quantization processor quantizes positions of one or more 3D blocks (e.g., slices) spatially partitioned by the spatial partitioner 51004. In this case, the quantization processor may perform some or all of the operations of the quantization unit 40001 of FIG. 4 , or perform some or all of the operations of the quantization processor 12001 of FIG. 12 . When the quantization processor is further provided between the spatial partitioner 51004 and the voxelization processor 53001, the quantization processor 51003 of FIG. 15 may or may not be omitted.

The voxelization processor 53001 according to the embodiments performs voxelization based on the positions of the one or more spatially partitioned 3D blocks (e.g., slices) or the quantized positions thereof. Voxelization refers to the minimum unit expressing position information in a 3D space. Points of point cloud content (or 3D point cloud video) according to embodiments may be included in one or more voxels. According to embodiments, one voxel may include one or more points. In an embodiment, in the case where quantization is performed before voxelization is performed, a plurality of points may belong to one voxel.

In the present specification, when two or more points are included in one voxel, the two or more points are referred to as duplicated points. That is, in the geometry encoding process, overlapping points may be generated through geometry quantization and voxelization.

The voxelization processor 53001 according to the embodiments may output the duplicated points belonging to one voxel to the octree generator 53002 without merging the same, or may merge the multiple points into one point and output the merged point to the octree generator 53002.

The octree generator 53002 according to the embodiments generates an octree based on a voxel output from the voxelization processor 53001.

The geometry information predictor 53003 according to the embodiments predicts and compresses geometry information based on the octree generated by the octree generator 53002, and outputs the predicted and compressed information to the arithmetic coder 53004. In addition, the geometry information predictor 53003 reconstructs the geometry based on the positions changed through compression, and outputs the reconstructed (or decoded) geometry to the LOD configuration unit 53007 of the attribute encoder 51007. The reconstruction of the geometry information may be performed in a device or component separate from the geometry information predictor 53003. In another embodiment, the reconstructed geometry may also be provided to the attribute transformation processor 53006 of the attribute encoder 51007.

The color transformation processor 53005 of the attribute encoder 51007 corresponds to the color transformation unit 40006 of FIG. 4 or the color transformation processor 12008 of FIG. 12 . The color transformation processor 53005 according to the embodiments performs color transformation coding of transforming color values (or textures) included in the attributes provided from the data input unit 51001 and/or the spatial partitioner 51004. For example, the color transformation processor 53005 may transform the format of color information (e.g., from RGB to YCbCr). The operation of the color transformation processor 53005 according to the embodiments may be optionally applied according to color values included in the attributes. In another embodiment, the color transformation processor 53005 may perform color transformation coding based on the reconstructed geometry. For details of the geometry reconstruction, refer to the description of FIGS. 1 to 9 .

The attribute transformation processor 53006 according to the embodiments may perform attribute transformation of transforming attributes based on positions on which geometry encoding has not been performed and/or the reconstructed geometry.

The attribute transformation processor 53006 may be referred to as a recoloring unit.

The operation of the attribute transformation processor 53006 according to the embodiments may be optionally applied according to whether duplicated points are merged. According to an embodiment, merging of the duplicated points may be performed by the voxelization processor 53001 or the octree generator 53002 of the geometry encoder 51006.

In the present specification, when points belonging to one voxel are merged into one point in the voxelization processor 53001 or the octree generator 53002, the attribute transformation processor 53006 performs an attribute transformation. Take an example.

The attribute transformation processor 53006 performs an operation and/or method identical or similar to the operation and/or method of the attribute transformation unit 40007 of FIG. 4 or the attribute transformation processor 12009 of FIG. 12 .

According to embodiments, the geometry information reconstructed by the geometry information predictor 53003 and the attribute information output from the attribute transformation processor 53006 are provided to the LOD configuration unit 53007 for attribute compression.

According to embodiments, the attribute information output from the attribute transformation processor 53006 may be compressed by one or a combination of two or more of RAHT coding, LOD-based predictive transform coding, and lifting transform coding based on the reconstructed geometry information.

Hereinafter, it is assumed that attribute compression is performed by one or a combination of the LOD-based predictive transform coding and the lifting transform coding as an embodiment. Thus, a description of the RAHT coding will be omitted. For details of the RAHT transform coding, refer to the descriptions of FIGS. 1 to 9 .

The LOD configuration unit 53007 according to the embodiments generates a Level of Detail (LOD).

The LOD is a degree representing the detail of the point cloud content. As the LOD value decreases, it indicates that the detail of the point cloud content is degraded. As the LOD value increases, it indicates that the detail of the point cloud content is enhanced. Points of the reconstructed geometry (i.e., the reconstructed positions) may be classified according to the LOD.

In an embodiment, in the predictive transform coding and the lifting transform coding, points may be divided into LODs and grouped.

This operation may be referred to as an LOD generation process, and a group having different LODs may be referred to as an LOD₁ set. Here, 1 denotes the LOD and is an integer starting from 0. LOD₀ is a set consisting of points with the largest distance therebetween. As 1 increases, the distance between points belonging to LOD₁ decreases.

When the LOD₁ set is generated by the LOD configuration unit 53007, the neighbor point configuration unit 53008 according to the embodiment may find X (>0) nearest neighbor (NN) points in a group having the same or lower LOD (i.e., a large distance between nodes) based on the LOD₁ set and register the same in the predictor as a neighbor set. X is the maximum number of points that may be set as neighbors. X may be input as a user parameter (also referred to as encoder option), or be signaled in signaling information through the signaling processor 51005 (e.g., the lifting_num_pred_nearest_neighbours field signaled in the APS).

Referring to FIG. 9 as an example, neighbors of P3 belonging to LOD₁ are found in LOD₀ and LOD₁. For example, when the maximum number (X) of points that may be set as neighbors is 3, three nearest neighbor nodes of P3 may be P2 P4 P6. These three nodes are registered as in the predictor of P3 as a neighbor set. In an embodiment, among the registered nodes, the neighbor node P4 is the closest to P3 in terms of distance, then P6 is the next nearest node, and P2 is the farthest node among the three nodes. Here, X=3 is merely an embodiment configured to provide understanding of the present disclosure. The value of X may vary.

As described above, all points of the point cloud data may have a predictor, respectively.

The attribute information prediction unit 53009 according to embodiments predicts attribute values from neighbor points registered in a predictor and obtains a residual attribute value of a corresponding point based on the predicted attribute values. The residual attribute value is output to the residual attribute information quantization processor 53010.

Next, LOD generation and neighbor point search will be described in detail.

As described above, for attribute compression, the attribute encoder performs a process of generating LODs based on points of reconstructed geometry and searching for the nearest neighbor points of a point to be encoded based on the generated LODs. According to embodiments, even the attribute decoder of the reception device performs a process of generating LODs and searching for the nearest neighbor points of a point to be decoded based on the generated LODs.

According to embodiments, the LOD configuration unit 53007 may configure one or more LODs using one or more LOD generation methods (or LOD configuration methods).

According to embodiments, an LOD generation method used in the LOD configuration unit 53007 may be input as a user parameter or may be signaled in signaling information through the signaling processor 51005. For example, the LOD generation method may be signaled in an APS.

According to embodiments, the LOD generation methods may be classified into an octree-based LOD generation method, a distance-based LOD generation method, and a sampling-based LOD generation method.

FIG. 18 is a diagram illustrating an example of generating LODs based on an octree according to embodiments.

According to embodiments, when LODs are generated based on an octree, each depth level of the octree may be matched to each LOD as illustrated in FIG. 18 . That is, the octree-based LOD generation method is a method of generating LODs using characteristics in which a detail representing point cloud data gradually increases as a depth level increases (i.e., a direction from a root to a leaf) in an octree structure. According to embodiments, an octree-based LOD configuration may be performed from a root node to a leaf node or, conversely, from the leaf node to the root node.

The distance-based LOD generation method according to embodiments is a method of arranging points using a Morton code and generating LODs based on a distance between the points.

The sampling-based LOD generation method according to embodiments is a method of arranging points using a Morton code and classifying every k-th point as a lower LOD that may be a candidate of a neighbor set. That is, during sampling, every k-th point may be selected and classified as a lower candidate set belonging to LOD₀ to LOD₁₋₁, and the remaining points may be registered in an LOD₁ set. That is, the selected points become a candidate group that may be selected as a neighbor point set of the points registered in the LOD₁ set. k may differ according to point cloud content. Here, the points may be points of a captured point cloud or points of reconstructed geometry.

In the present disclosure, a lower candidate set corresponding to LOD₀ to LOD₁₋₁ based on the LOD₁ set will be referred to as a retained set or an LOD retained set. LOD₀ is a set consisting of points with the largest distance therebetween. As 1 increases, the distance between points belonging to LOD₁ decreases.

According to embodiments, points in the LOD₁ set are also arranged based on a Morton code order. In addition, points included in each of the LOD₀ to LOD₁₋₁ sets are also arranged based on a Morton code order.

FIG. 19 is a diagram illustrating an example of arranging points of a point cloud in a Morton code order according to embodiments.

That is, a Morton code of each point is generated based on x, y, and z position values of each point of a point cloud. When Morton codes of points of the point cloud are generated through this process, the points of the point cloud may be arranged in a Morton code order. According to embodiments, the points of the point cloud may be arranged in ascending order of the Morton codes. The order of points arranged in ascending order of the Morton codes may be referred to as a Morton order.

The LOD configuration unit 53007 according to embodiments may generate LODs by performing sampling upon points arranged in Morton order.

The LOD configuration unit 53007 generates the LOD₁ set by applying at least one of the octree-based LOD generation method, the distance-based LOD generation method, or the sampling-based LOD generation method, the neighbor point set configuration unit 53008 may search for X(>0) nearest neighbor (NN) points in a group having the same or lower LOD (i.e. a large distance between nodes) based on the LOD₁ set and register the X NN points as a neighbor point set in a predictor.

In this case, since much time is consumed to search for all points in order to configure the neighbor point set, an embodiment of searching for neighbor points within a neighbor point search range including only partial points is provided. The search range refers to the number of points and may be 128, 256, or another value. According to embodiments, information related to the search range may be set in the neighbor point set configuration unit 53008 or may be input as the user parameter. Alternatively, the information about the search range may be signaled in signaling information through the signaling processor 51005 (e.g. a lifting_search_range field signaled in the APS).

FIG. 20 is a diagram illustrating an example of searching for neighbor points in a search range based on LOD according to embodiments. Arrows illustrated in the drawing indicate a Morton order according to embodiments.

In FIG. 20 , in an embodiment, an index list includes an LOD set (i.e., LOD₁) to which points to be encoded belong and a retained list includes at least one lower LOD set (e.g., LOD₀ to LOD₁₋₁) based on the LOD₁ set.

According to embodiments, the points of the index list are arranged in ascending order based on the size of a Morton code, and the points of the retained list are also arranged in ascending order based on the size of the Morton code. Therefore, the foremost point of the points arranged in Morton order in the index list and retained list has the smallest size of the Morton code.

The neighbor point set configuration unit 53008 according to embodiments may search for a point having a Morton code nearest to a Morton code of a point Px among points located before the point Px in order (i.e., points having Morton codes smaller than or equal to the Morton code of the point Px) among points belonging to LOD₀ to LOD₁₋₁ sets and/or points belonging to the LOD₁ set, in order to generate a neighbor point set of the point Px (i.e., a point to be encoded or a current point) belonging to the LOD₁ set. In the present disclosure, the searched point will be referred to as Pi or a center point.

According to embodiments, when searching for the center point Pi, the neighbor point set configuration unit 53008 may search for the point Pi having a Morton code nearest to a Morton code of the point Px among all points located before the point Px or search for the point Pi having the Morton code nearest to the Morton code of the point Px among points in a search range. In the present disclosure, the search range may be configured by the neighbor point set configuration unit 53008 or may be input as a user parameter. In addition, information about the search range may be signaled in signaling information through the signaling processor 51005. The present disclosure provides an embodiment of searching for the center point Pi in the retained list when the number of LODs is plural and searching for the central point Pi in the index list when the number of LODs is one. For example, when the number of LODs is 1, the search range may be determined based on the position of a current point in a list arranged with Morton codes.

The neighbor point set configuration unit 53008 according to embodiments compares distance values between the point Px and points belonging to a neighbor point search range located before the searched (or selected) center point Pi (i.e., on the left side of the center point in FIG. 20 ) and after the searched (or selected) center point Pi (i.e., on the right side of the center point in FIG. 20 ). The neighbor point set configuration unit 53008 may register X (e.g., 3) NN points as a neighbor point set. In an embodiment, the neighbor point search range is the number of points. The neighbor point search range according to embodiments may include one or more points located before (i.e., in front of) and/or after (i.e., behind) the center point Pi in Morton order. X is the maximum number of points that may be registered as neighbor points.

According to embodiments, information about the neighbor point search range and information about the maximum number X of points that may be registered as neighbor points may be configured by the neighbor point set configuration unit 53008 or may be input as a user parameter or signaled in signaling information through the signaling processor 51005 (e.g., a lifting_search_range field and a lifting_num_pred_nearest_neighbours field signaled in an APS). According to embodiments, an actual search range may be a value obtained by multiplying the value of the lifting_search_range field by 2 and then adding the center point to the resultant value (i.e., (value of the lifting_search_range field*2)+center point), a value obtained by adding the center value to the value of the lifting_search_range field (i.e., value of lifting_search_range field+center point), or the value of the lifting_search_range field. The present disclosure provides an embodiment of searching for neighbor points of the point Px in the retained list when the number of LODs is plural and searching for neighbor points of the point Px in the index list when the number of LODs is one.

For example, if the number of LODs is 2 or more and the information about the search range (e.g., lifting_search_range field) is 128, the actual search range includes 128 points before the center point Pi, 128 points after the center point Pi, and the center point Pi in the retained list arranged with Morton codes. As another example, if the number of LODs is 1 and the information about the search range is 128, the actual search range includes 128 points before the center point Pi and the center point Pi in the index list arranged with Morton codes. As another example, if the number of LODs is 1 and the information about the search range is 128, the actual search range includes 128 points before the current point Px in the index list arranged with Morton codes.

According to embodiments, the neighbor point set configuration unit 53008 may compare distance values between points within the actual search range and the point Px and register X NN points as a neighbor point set of the point Px.

On the other hand, attribute characteristics of content may appear differently depending on an object from which content is captured, a captured scheme, or equipment used for capturing content.

FIGS. 21A and 21B are diagrams illustrating examples of point cloud content according to embodiments.

FIG. 21A illustrates an example of dense point cloud data obtained by capturing an object with a 3D scanner, and there may be a high correlation between attributes of the object. However, even when the point cloud data is composed of one object as shown in FIG. 21A, the density of points of the point cloud data may affect the similarity of prediction performed based on neighbor points.

FIG. 21B illustrates an example of sparse point cloud data obtained by capturing a wide region with a LiDAR device, and the attribute correlation between points may be low. An example of dense point cloud data may be a still image, and an example of sparse point cloud data may be a drone or an autonomous vehicle. As shown in FIG. 21B, when point cloud data is composed of multiple objects, particularly when a large region is captured with a real-time LiDAR device, the density of the points of the captured point cloud data is low. Accordingly, similarity of the neighbor points may be low, which may lower compression efficiency.

In this way, attribute characteristics of content may appear differently depending on an object from which content is captured, a captured scheme, or equipment used for capturing content. If neighbor point search is performed to configure a neighbor point set when encoding attributes without taking different attribute characteristics into account, distances between a corresponding point and registered neighbor points may not all be adjacent. For example, when X (e.g., 3) NN points are registered as the neighbor point set after comparing distance values between the point Px and points belonging to the neighbor point search range before and after the center point Pi, at least one of the X registered neighbor points may be far away from the point Px. In other words, at least one of the X registered neighbor points may not be an actual neighbor point of the point Px.

This phenomenon is more likely to occur in the sparse point cloud data than in the dense point cloud data. For example, as illustrated in FIG. 21A, if there is one object in content, the one object has color continuity/similarity and is densely captured, and a captured area is small, there may be content having a high attribute correlation between points even when the points are a little apart from a neighbor point. Conversely, as illustrated in FIG. 21B, if a considerably wide area is sparsely captured with a LiDAR device, there may be content having a color correlation only when the distance to the neighbor point is within a specific range. Therefore, when encoding attributes of the sparse point cloud data as illustrated in FIG. 21B, some of the neighbor points registered through neighbor point search may not be actual neighbor points of the point to be encoded.

This phenomenon has a high probability of occurring when points are arranged in Morton order when generating LOD. That is, although the Morton order quickly arranges neighbor points, a jumping section (i.e., intermittent long lines in FIG. 19 ) occurs due to a zigzag scan feature of the Morton code and then locations of points may be greatly changed. In this case, some of the neighbor points registered through the neighbor point search within the search range may not be the actual NN points of the point to be encoded.

FIGS. 22A and 22B are diagrams illustrating examples of an average distance, a minimum distance, and a maximum distance of points belonging to a neighbor point set according to embodiments.

FIG. 22A illustrates an example of the 100th frame of content called FORD and FIG. 22B illustrates an example of the first frame of content called QNX.

FIG. 22A and FIG. 22B are exemplary embodiments to aid in understanding those skilled in the art. FIG. 22A and FIG. 22B may be different frames of the same content or specific frames of different content.

For convenience of explanation, the frame illustrated in FIG. 22A is referred to as a first frame and the frame illustrated in FIG. 22B is referred to as a second frame.

In the first frame of FIG. 22A, the total number of points is 80265, there are 4 points in which only one NN point is registered, there are 60 points in which 2 NN points are registered, and there are 80201 points in which 3 NN points are registered. That is, the maximum number of points that may be registered as the NN points is 3 but may be 1 or 2 depending on positions of points in the frame.

In the second frame of FIG. 22B, the total number of points is 31279, there are 3496 points in which only one NN is registered, there are 219 points in which 2 NN points are registered, and there are 27564 points are registered in which 3 NN points are registered.

In the first frame of FIG. 22A and the second frame of FIG. 22B, NN1 is the NN point, NN2 is the next-NN point, and NN3 is the third NN point. The maximum distance of NN2 in the first frame of FIG. 22A is 1407616 and the maximum distance of NN3 is 1892992, whereas the maximum distance of NN2 in the second frame of FIG. 22B is 116007040 and the maximum distance of NN3 is 310887696.

That is, it may be appreciated that there is a considerable difference in distance according to content or frame. Accordingly, some of the registered neighbor points may not be actual neighbor points.

In this way, if the distance difference between a point to be encoded and a registered neighbor point becomes large, an attribute difference between the two points is likely to be large. In addition, when prediction is performed based on the neighbor point set including these neighbor points and a residual attribute value is obtained, the residual attribute value may increase, resulting in an increase in a bitstream size.

In other words, characteristics of content or a frame may have an effect on configuration of the neighbor point set for attribute prediction and this may affect compression efficiency of attributes.

Therefore, in this disclosure, when configuring the neighbor point set in order to encode attributes of point cloud content, neighbor points are selected in consideration of an attribute correlation between points of the content, so that meaningless points are not selected as the neighbor point set. Then, since a residual attribute value decreases and the bitstream size is thereby reduced, compression efficiency of attributes is improved. In other words, the present disclosure improves compression efficiency of attributes using a method of restricting points that may be selected as the neighbor point set in consideration of the attribute correlation between points of content.

The present disclosure provides an embodiment of applying a maximum neighbor point distance (also referred to as a maximum NN distance) in order to consider an attribute correlation between points of content when configuring a neighbor point set in an attribute encoding process of point cloud content.

The present disclosure provides an embodiment of configuring the neighbor point set by applying a search range and/or a maximum NN distance when encoding attributes of point cloud content.

According to embodiments, the distance between points for selecting the nearest neighbor is less than or equal to the maximum neighbor point distance (also referred to as the maximum nearest neighbor distance).

For example, as a result of comparing distance values between a point Px and points belonging to a neighbor point search range before and after a center point Pi, points farther than the maximum NN distance among X (e.g., 3) NN points are not registered in the neighbor point set of the point Px. In other words, only points within the maximum NN distance among X (e.g., 3) NN points are registered in the neighbor point set of the point Px as a result of comparing distance values between the point Px and points belonging to the neighbor point search range before and after the center point Pi. For example, if one of the three points having the nearest distance is farther than the maximum NN distance, the farther-away point may be excluded and only the remaining two points may be registered in the neighbor point set of the point Px.

The neighbor point set configuration unit 53008 according to embodiments may apply the maximum NN distance according to attribute characteristics of content in order to achieve optimum compression efficiency of attributes regardless of the attribute characteristics of content. Here, the maximum NN distance may be calculated differently according to the LOD generation method (the octree-based, distance-based, or sampling-based LOD generation method). That is, the maximum NN distance may be applied differently to each LOD.

In the present disclosure, the maximum NN distance is used interchangeably with a maximum distance of a neighbor point or a maximum neighbor point distance. In other words, in the present disclosure, the maximum NN distance, the maximum distance of the neighbor point, and the maximum neighbor point distance have the same meaning.

In the present disclosure, the maximum NN distance may be obtained by multiplying a base neighbor point distance (referred to as a base distance or a reference distance) by NN_range as illustrated in Equation 5 below. Maximum Neighbor Point Distance=Base Neighbor Point Distance*NN_range  [Equation 5]

In Equation 5, NN_range is a range within which a neighbor point may be selected and may be referred to as a maximum range within which a neighbor point may be selected, a maximum neighbor point range, a neighbor point range, or a nearest neighbor range.

The neighbor point set configuration unit 53008 according to embodiments may set NN_range automatically or manually according to characteristics of content or set NN_range through input as a user parameter (also referred to as encoder option). In addition, information related to NN_range may be signaled in signaling information through the signaling processor 51005. The signaling information including information related to NN_range may be at least one of an SPS, an APS, a tile parameter set, or an attribute slice header.

When the NN_range is automatically calculated, the attribute decoder of the reception device may also automatically calculate the NN_range and apply the same to a neighbor point search.

When the information related to the NN_range is signaled in the signaling information, the attribute decoder of the reception device may calculate the maximum neighbor point distance based on the signaling information. In this case, neighbor points used in the attribute prediction in the attribute encoding may be reconstructed and applied to attribute decoding.

According to embodiments, the neighbor point set configuration unit 53008 may calculate/configure the base neighbor point distance by combining one or more of an octree-based method, a distance-based method, a sampling-based method, an average difference-based method of Morton codes for each LOD, and an average distance difference-based scheme for each LOD. According to embodiments, the method of calculating/configuring the base neighbor point distance and/or base neighbor point distance information may be signaled in signaling information (e.g., at least one of SPS, APS, TPS, or attribute slice header) through the signaling processor 51005.

Next, embodiments of acquiring a base neighbor point distance and a maximum neighbor point distance when LODs are generated based on an octree| will be described.

As illustrated in FIG. 18 , when the LOD configuration unit 53007 generates octree-based LODs, each depth level of the octree may be matched to each LOD.

The neighbor point set configuration unit 53008 according to embodiments may obtain a maximum neighbor point distance based on the octree-based LODs.

According to embodiments, when the LOD configuration unit 53007 generates the octree-based LODs, spatial scalability may be supported. With spatial scalability, a lower resolution point cloud, like a thumbnail with less decoder complexity and/or less bandwidth, may be accessed when a source point cloud is dense. For example, a spatial scalability function of geometry may be provided by a process of encoding or decoding occupancy bits only up to a selected depth level by adjusting a depth level of the octree during encoding/decoding of geometry. In addition, even during encoding/decoding of an attribute, the spatial scalability function of the attribute may be provided by a process of generating LODs from a selected depth level of the octree and configuring points on which encoding/decoding of the attribute is to be performed.

According to embodiments, for spatial scalability, the LOD configuration unit 53007 may generate the octree-based LODs and the neighbor point set configuration unit 53008 may perform neighbor point search based on the generated octree-based LODs.

When the neighbor point set configuration unit 53008 according to embodiments searches for neighbor points in previous LODs based on points belonging to a current octree-based generated LOD, a maximum neighbor point distance may be obtained by multiplying a base neighbor point distance (referred to as a base distance or a reference distance) by NN_range (i.e., base neighbor point distance*NN_range).

According to embodiments, a maximum distance (i.e., a diagonal distance) of one node in a specific octree-based generated LOD may be defined as the base distance (or a base neighbor point distance).

According to embodiments, when searching for neighbor points in previous LODs (e.g., LOD₀ to LOD₁₋₁ in the retained list) based on points belonging to a current LOD (e.g., LOD₁ set in the index list), a diagonal distance of a higher node (parent node) of an octree node of the current LOD may be a base distance for acquiring the maximum neighbor point distance.

According to an embodiment, the base distance, which is the diagonal distance (i.e., the maximum distance) of one node at a specific LOD, may be obtained as in Equation 6 below. Base distance=√{square root over (2^(lod) ² ×3)}  [Equation 6]

According to another embodiment, the base distance, which is the diagonal distance (i.e., the maximum distance) of one node at a specific LOD, may be obtained based on L2 as shown in Equation 7 below. L2-based base distance=2^(lod) ² ×3  [Equation 7]

In general, when calculating the distance between two points, the Manhattan distance calculation method or the Euclidean distance calculation method is used. The Manhattan distance will be referred to as an L1 distance and the Euclidean distance will be referred to as an L2 distance. A Euclidean space may be defined using the Euclidean distance and a norm corresponding to this distance will be referred to as a Euclidean norm or L2 norm. Norm is a method (function) of measuring the length or size of a vector.

FIG. 23A illustrates an example of acquiring a diagonal distance of an octree node of LOD₀. According to embodiments, when the example of FIG. 23A is applied to Equation 6, the base distance becomes V and, when the example of FIG. 23A is applied to Equation 7, the base distance becomes 3.

FIG. 23B illustrates an example of calculating a diagonal distance of an octree node of LOD₁. According to embodiments, when the example of FIG. 23B is applied to Equation 6, the base distance becomes √{square root over (12)} and, when the example of FIG. 23B is applied to Equation 7, the base distance becomes 12.

FIGS. 24A and 24B illustrate examples of a maximum range (NN_range) that may be selected as a neighbor point at each LOD. More specifically, FIG. 24A illustrates an example when NN_range is 1 at LOD₀ and FIG. 24B illustrates an example when NN_range is 3 at LOD₀. According to embodiments, NN_range may be set automatically or manually according to characteristics of content or may be set through input as a user parameter. Information related to NN_range may be signaled in signaling information. The signaling information including the information related to NN_range may be at least one of an SPS, an APS, a tile parameter set, or an attribute slice header. According to embodiments, the range NN_range that may be set as a neighbor point may be set to an arbitrary value (e.g., a multiple of the base distance) regardless of an octree node range.

According to embodiments, when the example of FIG. 24A is applied to Equations 5 and 6, the maximum neighbor point distance becomes √{square root over (3)}(=√{square root over (3)}*1) and, when the example of FIG. 24B is applied to Equation 5 and Equation 6, the maximum neighbor point distance becomes √{square root over (3)}(=√{square root over (3)}*3).

According to embodiments, when the example of FIG. 24A is applied to Equation 5 and Equation 7, the maximum neighbor point distance becomes 3 (=3*1) and, when the example of FIG. 24B is applied to Equation 5 and Equation 7, the maximum neighbor point distance is 9 (=3*3).

Next, embodiments of acquiring the base neighbor point distance and the maximum neighbor point distance when distance-based LODs are generated will be described.

According to embodiments, when configuring the distance-based LODs, the base neighbor point distance may be set as a distance used to configure points at a current LOD (i.e., LOD₁). That is, the base distance for each LOD may be set to a distance (dist2_(L)) applied to LOD generation at an L level of an LOD.

FIG. 25 illustrates examples of a base neighbor point distance belonging to each LOD according to embodiments.

Therefore, when configuring distance-based LODs, the maximum neighbor point distance may be obtained by multiplying a distance-based base neighbor point distance dist2_(L) by NN_range.

According to embodiments, NN_range may be set automatically or manually according to characteristics of content by the neighbor point set configuration unit 53008 or may be set through input as a user parameter. Information related to NN_range may be signaled in signaling information. The signaling information including the information related to NN_range may be at least one of an SPS, an APS, a tile parameter set, or an attribute slice header. According to embodiments, NN_range that may be set as a neighbor point may be set to an arbitrary value (e.g., a multiple of the base distance). According to embodiments, NN_Range may be adjusted according to a method of calculating a distance to the neighbor point.

Next, embodiments of acquiring a base neighbor point distance and a maximum neighbor point distance when sampling-based LODs are generated will be described.

According to embodiments, when sampling-based (i.e., decimation-based) LODs are generated, the base distance may be determined according to a sampling rate. According to embodiments, in a sampling-based LOD configuration method, Morton codes are generated based on position values of points, the points are arranged according to the Morton codes, and then points that do not correspond to the k-th point according to the arranged order are registered in a current LOD. Therefore, each LOD may have a different k and may be expressed as k_(L).

According to an embodiment, when LODs are generated by applying a sampling method to points arranged based on Morton codes, an average distance of consecutive k_(L)-th points at each LOD may be set to the base neighbor point distance at each LOD. That is, the average distance of consecutive k_(L)-th points at a current LOD arranged based on the Morton codes may be set to the base neighbor point distance of the current LOD. According to another embodiment, when LODs are generated by applying the sampling method to points arranged based on the Morton codes, a depth level of an octree may be estimated from the current LOD level, and a diagonal length of the node of the estimated octree depth level may be set to the base neighbor point distance. That is, the base neighbor point distance may be obtained by applying Equation 6 or 7 described above.

Therefore, when configuring sampling-based LODs, the maximum neighbor point distance may be obtained by multiplying the sampling-based base neighbor point distance by NN_range.

According to embodiments, NN_range may be automatically or manually set according to characteristics of content by the neighbor point set configuration unit 53008 or may be set through input as a user parameter. Information related to NN_range may be signaled in signaling information. The signaling information including the information related to NN_range may be at least one of an SPS, an APS, a tile parameter set, or an attribute slice header. According to embodiments, NN_range that may be set as a neighbor point may be set to an arbitrary value (e.g., a multiple of the base distance). According to embodiments, NN_Range may be adjusted according to a method of calculating a distance to the neighbor point.

In the present disclosure, the base neighbor point distance may be obtained using a method other than the above-described method of acquiring the base neighbor point distance.

For example, when configuring the LODs, the base neighbor point distance may be configured by calculating an average difference of Morton codes of sampled points. In addition, the maximum neighbor point distance may be obtained by multiplying the configured base neighbor point distance by NN_range.

As another example, the base neighbor point distance may be configured by calculating an average distance difference for currently configured LODs regardless of whether the distance-based method is used or the sampling-based method is used. In addition, the maximum neighbor point distance may be obtained by multiplying the configured base neighbor point distance by NN_range.

As another example, the base neighbor point distance for each LOD may be received as the user parameter and then applied when acquiring the maximum neighbor point distance. Thereafter, information about the received base neighbor point distance may be signaled in signaling information.

As described above, the base neighbor point distance may be obtained by applying the best base neighbor point distance calculation method according to the LOD configuration method. In another embodiment, the method of calculating the base neighbor point distance may be applied by selecting an arbitrarily desired method and signaling the selected method in the signaling information so as to use the method to restore points in the decoder of the reception device. According to embodiments, a method of calculating the maximum neighbor point distance that is suitable for an attribute of point cloud content and is capable of maximizing compression performance may be used.

Next, embodiments of automatically calculating a maximum neighbor point range (NN_range) will be described.

According to embodiments, the method of obtaining the maximum neighbor point range may vary according to the LOD generation method.

According to embodiments, the neighbor point set configurator 53008 may automatically calculate the maximum neighbor point range according to the density, or calculate the maximum neighbor point range automatically by inferring the density according to the length of the axis and the number of points.

FIG. 26 is a flowchart illustrating automatic calculation of the maximum neighbor point range based on the density according to an embodiment of the present disclosure.

First, some of the points are scanned to calculate a base neighbor point distance for each LOD (operation 55001). Here, according to an embodiment, it is assumed that the base neighbor point distance for each LOD is greater than 0 (>0). In the present disclosure, for simplicity, the base neighbor point distance for each LOD is referred to as dist2₀.

According to embodiments, the base neighbor point distance may be obtained differently depending on the LOD generation method.

For example, when LODs are generated based on an octree, the diagonal distance (i.e., the maximum distance) of one node in a specific LOD may be set as the base neighbor point distance (e.g., see Equation 6 or 7). According to embodiments, when there is a plurality of LODs, the diagonal distance of the upper node (parent node) of the octree node of the current LOD may be set as the base neighbor point distance.

For example, when LODs are generated based on the distance, the base neighbor point distance may be set to a distance used to construct points at the level of the current LOD (i.e., LOD₁). That is, the base neighbor point distance for each LOD may be set to the distance dist2_(L) applied to the LOD generation at the LOD L level (see FIG. 25 ).

For example, when LODs are generated by applying a sampling method to points sorted based on the Morton code, the average distance of k_(L)-th consecutive points in each LOD may be set as the base neighbor point distance in each LOD. That is, the average distance of the k_(L)-th consecutive points in the current LOD sorted based on the Morton code may be set as the base neighbor point distance of the current LOD. As another example, when LODs are generated by applying a sampling method to points sorted based on the Morton code, the depth level of the octree may be estimated from the current LOD level, and the diagonal length of the node of the estimated octree depth level may be set as the base neighbor point distance. In this case, the base neighbor point distance may be acquired by applying Equation 6 or 7.

According to embodiments, the number of points selected per LOD in order to calculate the base neighbor point distance may be one out of four, or may be selected in consideration of other intervals.

Once the base neighbor point distance is calculated in operation 55001, the diagonal length of the bounding box of the points is calculated (operation 55002). In the present disclosure, for simplicity, the diagonal length of the bounding box will be referred to as BBox_diagonal_dist or BBox_diagonal_length.

According to an embodiment, the bounding box may be set by scanning point cloud data. According to another embodiment, the bounding box may be inferred and calculated with reference to the octree depth for construction of the octree.

A density rate (or density_estimation) may be estimated based on the base neighbor point distance calculated in operation 55001 and the diagonal length of the bounding box calculated in operation 55002 (operation 55003).

In an embodiment, the density rate may be acquired by dividing the base neighbor point distance by the diagonal length of the bounding box (density_rate=dist2₀/BBox_diagonal_dist). In this case, as the density rate increases, the density decreases.

In another embodiment, the density rate may be acquired by dividing the diagonal length of the bounding box by the base neighbor point distance (density_rate=BBox_diagonal_dist/dist2₀). In this case, in setting the maximum neighbor point range according to the density rate, the value of Kn and the sign may be changed. In this case, as the density rate decreases, the density decreases. According to embodiments, the value of Kn may be a table value used to set the maximum neighbor point range according to the calculated value obtained by automatically calculating the maximum neighbor point range.

Once the density rate is obtained in operation 55003, the maximum neighbor point range is set according to the density rate (operation 55004).

According to embodiments, when the density rate is greater than Kn (where n>=0 and Kn<1), the value of n or n+1 may be set as the maximum neighbor point range (n: density_rate>Kn (n>=0, Kn<1)).

According to embodiments, the value of Kn may be a table value used to set the maximum neighbor point range according to the calculated density rate in automatically calculating the maximum neighbor point range.

According to embodiments, the value of Kn may be set to a default according to the LOD generation method or may be set differently according to a user input. That is, information related to the value of Kn may be variably changed and signaled in the signaling information, or a fixed value may be preset in the attribute encoder/decoder by default.

For example, assuming that K1=0.000001 and the density rate is greater than 0.000001, the maximum neighbor point range (NN_range) is 1.

According to embodiments, the maximum neighbor point range information automatically calculated according to the density rate may be transmitted in signaling information. For example, the signaling information including the maximum neighbor point range information may be at least one of an SPS, an APS, a tile parameter set, or an attribute slice header.

FIG. 27 is a flowchart illustrating automatic calculation of the maximum neighbor point range based on the density according to another embodiment of the present disclosure. In the embodiment of FIG. 27 , the maximum neighbor point range is calculated by inferring the density according to the axis length and the number of points.

According to embodiments, the density may be inferred based on at least one of the minimum axis length of the bounding box, the maximum axis length of the bounding box, and the middle axis length of the bounding box.

FIG. 27 illustrates an embodiment of acquiring the maximum neighbor point range based on the minimum axis length of the bounding box and the number of points.

That is, the minimum axis length of the bounding box of the points is calculated (operation 57001). In the present disclosure, for simplicity, the minimum axis length of the bounding box is referred to as BBox_min_axis_length.

The density rate (density_rate or density_estimation) may be estimated based on the number of points and the minimum axis length of the bounding box calculated in operation 57001 (operation 57002).

In an embodiment, the density rate may be acquired by dividing the minimum axis length of the bounding box by the number of points (density_rate=BBox_min_axis_length/number of points). In this case, as the density rate increases, the density decreases.

Once the density rate is obtained in operation 57002, the maximum neighbor point range is set according to the density rate (operation 57003).

According to embodiments, when the density rate is greater than Kn (where n>=0 and Kn<1), the value of n or n+1 may be set as the maximum neighbor point range (n: density_rate>Kn (n>=0, Kn<1)).

According to embodiments, the value of Kn may be a table value used to set the maximum neighbor point range according to the calculated density rate in automatically calculating the maximum neighbor point range.

According to embodiments, the value of Kn may be set to a default according to the LOD generation method or may be set differently according to a user input. That is, information related to the value of Kn may be variably changed and signaled in the signaling information, or a fixed value may be preset in the attribute encoder/decoder by default.

For example, assuming that K1=0.05 and the density rate is greater than 0.05, the maximum neighbor point range (NN_range) is 1.

According to another embodiment, the density rate may be estimated based on the maximum axis length of the bounding box and the number of points, or may be estimated based on the middle axis length of the bounding box and the number of points. Then, the maximum neighbor point range is calculated based on the density rate. In this case, the method of calculating the maximum neighbor point range is the same as the method of calculating the maximum neighbor point range based on the minimum axis length of the above-described bounding box.

According to embodiments, the method of calculating the maximum neighbor point range that may match the attribute of point cloud content and maximize compression performance may be used.

According to embodiments, any desired method of calculating the maximum neighbor point range may be selected and applied, or a combination of one or more methods may be applied. Alternatively, information about whether to perform automatic calculation may be signaled and transmitted in the signaling information. According to embodiments, when the information about whether to perform automatic calculation indicates automatic calculation, the attribute decoder of the reception device may automatically calculate the maximum neighbor point range.

According to embodiments, information about a base neighbor point distance calculation method (e.g., nn_base_distance_calculation_method_type), base neighbor point distance information (e.g., nn_base_distance), maximum neighbor point range information (e.g., nearest_neighbor_max_range), minimum neighbor point range information (e.g., nearest_neighbor_min_range), information about how to apply the maximum neighbor point distance (e.g., nn_range_filtering_location_type), information about whether to automatically calculate the maximum neighbor point range (e.g., automatic_nn_range_calculation_flag), information about a method of calculating the maximum neighbor point range (e.g., automatic_nn_range_method_type), and information related to the value of Kn for the automatic maximum neighbor point range (e.g., automatic_max_nn_range_in_table, automatic_nn_range_table_k) may be referred to as neighbor point selection-related option information. The neighbor point selection-related option information may be signaled and transmitted in signaling information. In an embodiment, the signaling information may be at least one of a sequence parameter set, an attribute parameter set, a tile parameter set, or an attribute slice header.

According to embodiments, the neighbor point set configurator 53008 and/or the signaling processor 51005 may set a base neighbor point distance calculation method in the signaling information according to the LOD generation method (or the LOD configuration method) (e.g., nn_base_distance_calculation_method_type). According to embodiments, the base neighbor point distance calculation method may include an octree-based base neighbor point distance calculation, a distance-based base neighbor point distance calculation, a sampling-based base neighbor point distance calculation, a base neighbor point distance calculation based on the average difference in Morton code between LODs, a base neighbor point distance calculation based on an average distance difference between LODs, and a base neighbor point distance calculation according to an input base neighbor point distance.

According to embodiments, the base neighbor point distance calculated according to a base neighbor point distance calculation method may be applied to the calculation of the maximum neighbor point range. In addition, the base neighbor point distance calculation method may be signaled and transmitted in signaling information. In this case, the attribute decoder may calculate the maximum neighbor point range based on the signaling information and apply the same to the maximum neighbor point distance.

According to embodiments, the neighbor point set configurator 53008 and/or the signaling processor 51005 may receive the base neighbor point distance information (base_distance) as a user parameter (or encoder option) and apply the same to the calculation of the maximum neighbor point distance and/or the maximum neighbor point range. In addition, when the base neighbor point distance information is signaled in the signaling information, the attribute decoder of the receiving device may calculate the maximum neighbor point distance and/or maximum neighbor point range based on the signaling information.

According to embodiments, the neighbor point set configurator 53008 and/or the signaling processor 51005 may signal the maximum neighbor point range information in the signaling information, and the attribute decoder of the reception device may calculate the maximum neighbor point distance based on the signaling information. According to embodiments, the maximum neighbor point range may be set differently for each LOD.

According to embodiments, the neighbor point set configurator 53008 and/or the signaling processor 51005 may signal the neighbor point minimum range information in the signaling information, and the attribute decoder of the reception device may signal may calculate the maximum neighbor point distance based on the signaling information. According to embodiments, the minimum neighbor point range may be set differently for each LOD.

According to embodiments, the neighbor point set configurator 53008 and/or the signaling processor 51005 may receive information indicating whether to automatically calculate the maximum neighbor point range, or the minimum neighbor point range, or both the maximum and minimum neighbor point ranges as a user parameter (or referred to as an encoder option), and signal information indicating whether to perform the automatic calculation in the signaling information.

According to embodiments, when the neighbor point set configurator 53008 and/or the signaling processor 51005 automatically calculate the maximum neighbor point range, it may receive the value of Kn as a user parameter (or encoder option), and signal information related to the value of Kn in the signaling information. According to embodiments, the value of Kn may be a table value used to set the maximum neighbor point range according to the calculated value obtained by automatically calculating the maximum neighbor point range. According to embodiments, when the value of the information about whether to perform the automatic calculation is TRUE, the attribute decoder of the reception device may use the information related to the value of Kn signaled in the signaling information to determine the maximum neighbor point range.

According to embodiments, in automatically calculating the maximum neighbor point range, the neighbor point set configurator 53008 and/or the signaling processor 51005 may receive information about the method of calculating the maximum neighbor point range as a user parameter (or an encoder option). In addition, the information about the maximum neighbor point range calculation method (e.g., automatic_nn_range_method_type) may be signaled in the signaling information. According to embodiments, the methods of automatic calculation of the maximum neighbor point range may include a method of calculating the maximum neighbor point range according to the density (based on the denominator bounding box diagonal length or the numerator of the bounding box diagonal length), and a method of inferring the density based on the axis length and the number of points and calculating the maximum neighbor point range (based on the maximum, minimum, or middle axis of the bounding box). According to embodiments, the neighbor point set configurator 53008 may automatically calculate the maximum neighbor point range using the method of calculating the maximum neighbor point range according to the density, and/or the method of inferring the density based on the axis length and the number of points and calculating the maximum neighbor point range as an automatic calculation method. According to embodiments, when the value of the information about whether to perform the automatic calculation is TRUE, the attribute decoder of the reception device may use determine the maximum neighbor point range based on the information about the maximum neighbor point range calculation method signaled in the signaling information.

According to embodiments, the neighbor point set configurator 53008 may calculate the maximum neighbor point distance based on the base neighbor point distance (base_distance) and the maximum neighbor point range.

According to embodiments, the neighbor point set configurator 53008 may register only one or more points having a distance shorter than the calculated maximum neighbor point distance as a neighbor point set of the corresponding point.

According to embodiments, the neighbor point set configurator 53008 may receive, as a user parameter (or an encoder option), a method of applying the maximum neighbor point distance (e.g., nn_range_filtering_location_type), and signal, in signaling information, the method of applying the maximum neighbor point distance. According to embodiments, the method of applying the maximum neighbor point distance may include a method by which a distance between points is calculated and a point outside the maximum neighbor point distance is not selected in selecting neighbor points, and a method by which all neighbor points are registered by calculating a distance between the points, and points beyond the maximum neighbor point distance are removed among the registered points. According to embodiments, the attribute decoder of the reception device may configure a neighbor point set by applying the information about the method of applying the maximum neighbor point distance signaled in the signaling information (e.g., nn_range_filtering_location_type) to a neighbor point search.

The LOD configuration method, the base neighbor point distance acquisition method, the maximum neighbor point range (NN_range) acquisition method, and the maximum neighbor point distance acquisition method described above may be applied in the same or similar manner when the attribute decoder of the reception device configures a neighbor point set and LODs for predicting transform or lifting transform.

According to an embodiment, if the LOD₁ set is generated and the maximum neighbor point distance is determined based on the base neighbor point distance and the maximum neighbor point range (NN_range) as described above, the neighbor point set configuration unit 53008 searches for X (e.g., 3) NN points among points within a search range in a group having the same or lower LOD (i.e., a large distance between nodes) based on the LOD₁ set. Then the neighbor point set configuration unit 53008 may register only NN points within the maximum neighbor point distance among the X (e.g., 3) NN points as a neighbor point set. Therefore, the number of NN points registered as the neighbor point set is equal to or smaller than X. In other words, NN points not within the maximum neighbor point distance among the X NN points are not registered as the neighbor point set and are excluded from the neighbor point set. For example, if two of the three NN points are not within the maximum neighbor point distance, the two NN points are excluded and only the other NN point, i.e., one NN point, is registered as the neighbor point set.

According to another embodiment, if the LOD₁ set is generated and the maximum neighbor point distance is determined based on the base neighbor point distance and the maximum neighbor point range (NN_range) as described above, the neighbor point set configuration unit 53008 may search for X (e.g., 3) NN points within the maximum neighbor point distance among points within the search range in a group having the same or lower LOD (i.e., a large distance between nodes) based on the LOD₁ set and register the X NN points as the neighbor point set.

That is, the number of NN points that may be registered as the neighbor point set may vary according to a timing (or position) of applying the maximum neighbor point distance. In other words, the number of NN points registered as the neighbor point set may differ according to whether the maximum neighbor point distance is applied after searching for X NN points through neighbor point search or the maximum neighbor point distance is applied when calculating a distance between points. X is the maximum number that may be set as a neighbor point and may be input as a user parameter or signaled in signaling information through the signaling processor 51005 (e.g., the lifting_num_pred_nearest_neighbours field signaled in the APS).

FIG. 28 is a diagram illustrating an example of searching for neighbor points by applying a search range and a maximum neighbor point distance according to embodiments. Arrows illustrated in the drawing indicate a Morton order according to embodiments.

In FIG. 28 , in an embodiment, an index list includes an LOD set (i.e., LOD₁) to which points to be encoded belong and a retained list includes at least one lower LOD set (e.g., LOD₀ to LOD₁₋₁) based on an LOD₁ set.

According to embodiments, points in the index list and points in the retained list are arranged in ascending order based on the size of a Morton code. Therefore, the foremost point of the points arranged in Morton order in the index list and the retained list has the smallest size of the Morton code.

The neighbor point set configuration unit 53008 according to embodiments may search for a center point Pi having a Morton code nearest to a Morton code of a point Px among points located before the point Px in order (i.e., points having Morton codes smaller than or equal to the Morton code of the point Px) among points belonging to LOD₀ to LOD₁₋₁ sets and/or points belonging to the LOD₁ set, in order to register a neighbor point set of the point Px (i.e., a point to be encoded or a current point) belonging to the LOD₁ set.

According to embodiments, when searching for the center point Pi, the neighbor point set configuration unit 53008 may search for the point Pi having the Morton code nearest to the Morton code of the point Px among all points located before the point Px or search for the point Pi having the Morton code nearest to the Morton code of the point Px among points in a search range. In the present disclosure, the search range may be configured by the neighbor point set configuration unit 53008 or may be input as a user parameter (also referred to as encoder option). In addition, information related to the search range may be signaled in signaling information through the signaling processor 51005. The present disclosure provides an embodiment of searching for the center point Pi in the retained list when the number of LODs is plural and searching for the central point Pi in the index list when the number of LODs is one. For example, when the number of LODs is 1, the search range may be determined based on the position of a current point in a list arranged with Morton codes.

The neighbor point set configuration unit 53008 according to embodiments compares distance values between the point Px and points belonging to a neighbor point search range located before the searched (or selected) center point Pi (i.e., on the left side of the center point in FIG. 28 ) and after the searched (or selected) center point Pi (i.e., on the right side of the center point in FIG. 28 ). The neighbor point set configuration unit 53008 may select X (e.g., 3) NN points and register only points within the maximum neighbor point distance at an LOD to which the point Px belongs among the selected X points as a neighbor point set of the point Px. In an embodiment, the neighbor point search range is the number of points. The neighbor point search range according to embodiments may include one or more points located before (i.e., in front of) and/or after (i.e., behind) the center point Pi in Morton order. X is the maximum number of points that may be registered as neighbor points.

According to embodiments, information related to the neighbor point search range and information about the maximum number X of points that may be registered as neighbor points may be configured by the neighbor point set configuration unit 53008 or may be input as a user parameter or signaled in signaling information through the signaling processor 51005 (e.g., the lifting_search_range field and lifting_num_pred_nearest_neighbours field signaled in the APS). According to embodiments, an actual search range may be a value obtained by multiplying the value of the lifting_search_range field by 2 and then adding the center point to the resultant value (i.e., (value of the lifting_search_range field*2)+center point), a value obtained by adding the center value to the value of the lifting_search_range field (i.e., value of lifting_search_range field+center point), or the value of the lifting_search_range field. The present disclosure provides an embodiment of searching for neighbor points of the point Px in the retained list when the number of LODs is plural and searching for neighbor points of the point Px in the index list when the number of LODs is one.

For example, if the number of LODs is 2 or more and the information related to the search range (e.g., the lifting_search_range field) is 128, the actual search range includes 128 points before the center point Pi, 128 points after the center point Pi, and the center point Pi in the retained list arranged with Morton codes. As another example, if the number of LODs is 1 and the information related to the search range is 128, the actual search range includes 128 points before the center point Pi and the center point Pi in the index list arranged with Morton codes. As another example, if the number of LODs is 1 and the information related to the search range is 128, the actual search range includes 128 points before the current point Px in the index list arranged with Morton codes.

According to embodiments, the neighbor point set configuration unit 53008 compares the distance values between points in the actual search range and the point Px to search for X NN points and register only points within the maximum neighbor point distance at an LOD to which the point Px belongs among the X points as the neighbor point set of the point Px. That is, the neighbor points registered as the neighbor point set of the point Px are limited to points within the maximum neighbor point distance at the LOD to which the point Px belongs among the X points.

As described above, the present disclosure may provide an effect of enhancing compression efficiency of attributes by limiting points that may be selected as the neighbor point set in consideration of attribute characteristics (correlation) between points of point cloud content.

FIG. 29 is a diagram illustrating another example of searching for neighbor points by applying a search range and a maximum neighbor point distance according to embodiments. Arrows illustrated in the drawing indicate a Morton order according to embodiments.

Since the example of FIG. 29 is similar to that of FIG. 28 except for a position to which the maximum neighbor point distance is applied, a repetitive description thereof will be omitted herein. Therefore, for portions omitted or not described in FIG. 29 , refer to the description of FIG. 28 .

According to embodiments, points of the index list and points of the retained list are arranged in ascending order based on the size of a Morton code.

The neighbor point set configuration unit 53008 according to embodiments may search for a center point Pi having a Morton code nearest to a Morton code of a point Px among points located before the point Px in order (i.e., points having Morton codes smaller than or equal to the Morton code of the point Px) among points belonging to LOD₀ to LOD₁₋₁ sets and/or points belonging to the LOD₁ set, in order to register a neighbor point set of the point Px (i.e., a point to be encoded or a current point) belonging to the LOD₁ set.

The neighbor point set configuration unit 53008 according to embodiments compares distance values between the point Px and points belonging to a neighbor point search range located before the searched (or selected) center point Pi (i.e., on the left side of the center point in FIG. 29 ) and after the searched (or selected) center point Pi (i.e., on the right side of the center point in FIG. 29 ). The neighbor point set configuration unit 53008 may select X (e.g., 3) NN points within the maximum neighbor point distance at an LOD to which the point Px belongs and register the X points as the neighbor point set of the point Px.

The present disclosure provides an embodiment of searching for neighbor points of the point Px in an actual search range of the retained list when the number of LODs is plural and searching for the neighbor points of the point Px in the actual search range of the index list when the number of LODs is one.

For example, if the number of LODs is 2 or more and the information related to the search range (e.g., the lifting_search_range field) is 128, the actual search range includes 128 points before the center point Pi, 128 points after the center point Pi, and the center point Pi in the retained list arranged with Morton codes. As another example, if the number of LODs is 1 and the information related to the search range is 128, the actual search range includes 128 points before the center point Pi and the center point Pi in the index list arranged with Morton codes. As another example, if the number of LODs is 1 and the information related to the search range is 128, the actual search range includes 128 points before the current point Px in the index list arranged with Morton codes.

Upon comparing the distance values between points in the actual search range and the point Px, the neighbor point set configuration unit 53008 according to embodiments selects X (e.g., 3) NN points within the maximum neighbor point distance at an LOD to which the point Px belongs from among points in the actual search range and registers the X points as the neighbor point set of the point Px. That is, the neighbor points registered as the neighbor point set of the point Px are limited to points within the maximum neighbor point distance at the LOD to which the point Px belongs among the X points.

As described above, the present disclosure may provide an effect of enhancing compression efficiency of attributes by selecting the neighbor point set in consideration of attribute characteristics (correlation) between points of point cloud content.

According to the embodiments described above, when the neighbor point set is registered in each predictor of points to be encoded in the neighbor point set configuration unit 53008, the attribute information prediction unit 53009 predicts an attribute value of a corresponding point from one or more neighbor points registered in the predictor. As described above, when configuring the neighbor point set, the number of neighbor points included in the neighbor point set registered in each predictor is equal to or less than X (e.g., 3) by applying the maximum neighbor point distance. According to embodiments, a predictor of the point may register a ½ distance (=weight) based on a distance value to each neighbor point by a registered neighbor point set. For example, the predictor of the P3 node calculates a weight based on the distance value to each neighbor point by (P2 P4 P6) as the neighbor point set. According to embodiments, weights of neighbor points may be (1/√(P2-P3)², 1/√(P4-P3)², 1/√(P6-P3)²).

According to embodiments, when the neighbor point set is registered in the predictor, the neighbor point set configuration unit 53008 or the attribute information predicting unit 53009 may normalize a weight of each neighbor point by a total weight of neighbor points included in the neighbor point set.

For example, the weights of all neighbor points in the neighbor set of node P3 are added (total weight=1/√(P2-P3)²+1/√(P4-P3)²+1/√(P6-P3)²), and the weight of each neighbor point is divided by the sum of the weights (1/√(P2-P3)²/total weight, 1/√(P4-P3)²/total weight, 1/√(P6-P3)²/total weight). Thereby, the weight of each neighbor point is normalized

Then, the attribute information prediction unit 5301 may predict an attribute value through the predictor.

According to embodiments, the average of the values obtained by multiplying the attributes (e.g., color, reflectance, etc.) of neighbor points registered in the predictor by a weight (or a normalized weight) may be set as a predicted result (i.e., a predicted attribute value). Alternatively, an attribute of a specific point may be set as a predicted result (i.e., a predicted attribute value). According to embodiments, the predicted attribute value may be referred to as predicted attribute information. In addition, a residual attribute value (or residual attribute information or residual) may be obtained subtracting the predicted attribute value (or predicted attribute information) of the point from the attribute value (i.e., the original attribute value) of the point.

According to embodiments, compressed result values may be pre-calculated by applying various prediction modes (or predictor indexes), and then a prediction mode (i.e., a predictor index) generating the smallest bitstream may be selected from among the prediction modes.

Next, a process of selecting a prediction mode will be described in detail.

In this specification, a prediction mode has the same meaning as a predictor index (Preindex), and may be broadly referred to as a prediction method.

In an embodiment, the process of finding the most suitable prediction mode for each point and setting the found prediction mode in the predictor of the corresponding point may be performed by the attribute information prediction unit 53009.

According to embodiments, a prediction mode in which a predicted attribute value is calculated through a weighted average (i.e., an average obtained by multiplying the attributes of neighbor points set in the predictor of each point by a weight calculated based on the distance to each neighbor point) will be referred to as prediction mode 0. In addition, a prediction mode in which the attribute of the first neighbor point is set as a predicted attribute value will be referred to as prediction mode 1, a prediction mode in which the attribute of the second neighbor point is set as a predicted attribute value will be referred to as prediction mode 2, and a prediction mode in which the attribute of the third neighbor point is set as a predicted attribute value will be referred to as prediction mode 3. In other words, the value of the prediction mode (or predictor index) equal to 0 may indicate that the attribute value is predicted through the weighted average, and the value equal to 1 may indicate that the attribute value is predicted through the first neighbor node (i.e., the neighbor point). The value equal to 2 may indicate that the attribute value is predicted through the second neighbor node, and the value equal to 3 may indicate that the attribute value is predicted through the third neighboring node.

According to embodiments, a residual attribute value in prediction mode 0, a residual attribute value in prediction mode 1, a residual attribute value in prediction mode 2, and a residual attribute value in prediction mode 3 may be calculated, and a score or double score may be calculated based on each residual attribute value. Then, a prediction mode having the least calculated score may be selected and set as a prediction mode of the corresponding point.

According to embodiments, the process of finding the most suitable prediction mode among a plurality of prediction modes and setting the same as a prediction mode of a corresponding point may be performed when a preset condition is satisfied. Accordingly, when the preset condition is not satisfied, a pre-defined prediction mode, e.g., prediction mode 0, in which a prediction attribute value is calculated through a weighted average, may be set as the prediction mode of the point without performing the process of finding the most suitable prediction mode. In an embodiment, this process is performed for each point.

According to embodiments, the preset condition may be satisfied for a specific point when the difference in attribute elements (e.g., R, G, B) between neighbor points registered in the predictor of a point is greater than or equal to a preset threshold (e.g., lifting_adaptive_prediction_threshold), or when the differences in attribute elements (e.g., R, G, B) between the neighbor points registered in the predictor of the point are calculated, and the sum of the largest differences for the elements is greater than or equal to a preset threshold. For example, suppose that point P3 is the specific point, and points P2, P4, and P6 are registered as neighbor points of point P3. Additionally, suppose that, when differences in R, G, and B values between points P2 and P4, differences in R, G, and B values between points P2 and P6, and differences in R, G, and B values between points P4 and P6 are calculated, the largest difference in R value is obtained between points P2 and P4, the largest difference in G value is obtained between points P4 and P6, and the largest difference in B value is obtained between points P2 and P6. In addition, suppose that the difference in R value between points P2 and P4 is the largest among the largest difference in R value (between P2 and P4) and the largest difference in G value (between P4 and P6), and the largest difference in B value (between P2 and P6).

On these assumptions, when the difference in R value between points P2 and P4 is greater than or equal to a preset threshold, or when the sum of the difference in R value between points P2 and P4, the difference in G value between points P4 and P6, and the difference in B value between points P2 and P6 is greater than or equal to a preset threshold, a process of finding the most suitable prediction mode among a plurality of candidate prediction modes may be performed. In addition, the prediction mode (e.g., predIndex) may be signaled only when the difference in R value between points P2 and P4 is greater than or equal to a preset threshold, or the sum of the difference in R value between points P2 and P4, the difference in G value between points P4 and P6, and the difference in B value between points P2 and P6 is greater than or equal to a preset threshold.

According to another embodiment, the preset condition may be satisfied for a specific point when the maximum difference between values of an attribute (e.g., reflectance) of neighbor points registered in the predictor of the point is greater than or equal to a preset threshold (e.g., lifting_adaptive_prediction_threshold). For example, suppose that the difference in reflectance between points P2 and P4 is the largest among the difference in reflectance between points P2 and P4, the difference in reflectance between points P2 and P6, and the difference in reflectance between points P4 and P6.

On this assumption, the process of finding the most suitable prediction mode among a plurality of candidate prediction modes may be performed when the difference in reflectance between points P2 and P4 is greater than or equal to a preset threshold. In addition, the prediction mode (e.g., predIndex) may be signaled only when the difference in reflectance between points P2 and P4 is greater than or equal to the preset threshold.

According to embodiments, the selected prediction mode (e.g., predIndex) of the corresponding point may be signaled in attribute slice data. In this case, the transmitting side transmits a residual attribute value acquired based on the selected prediction mode and the receiving side acquires a predicted attribute value of a corresponding point based on the signaled prediction mode and adds the predicted attribute value and the received residual attribute value to restore an attribute value of the corresponding point.

In another embodiment, when the prediction mode is not signaled, the transmitting side may calculate a predicted attribute value based on a prediction mode (e.g., prediction mode 0) set as a default mode, and calculate and transmit a residual attribute value based on the difference between the original attribute value and the predicted attribute value. The receiving side may calculate a predicted attribute value based on a prediction mode (e.g., prediction mode 0) set as a default mode, and restore the attribute value by adding the value to the received residual attribute value.

According to embodiments, the threshold may be directly input or signaled in the signaling information through the signaling processor 51005 (e.g., the lifting_adaptive_prediction_threshold field signaled in the APS).

According to embodiments, when a preset condition is satisfied for a specific point as described above, predictor candidates may be generated. The predictor candidates are referred to as prediction modes or predictor indexes.

According to embodiments, prediction modes 1 to 3 may be included in the predictor candidates. According to embodiments, prediction mode 0 may or may not be included in the predictor candidates. According to embodiments, at least one prediction mode not mentioned above may be further included in the predictor candidates.

The prediction mode set for each point through the above-described process and the residual attribute value in the set prediction mode are output to the residual attribute information quantization processor 53010.

According to embodiments, the residual attribute information quantization processor 53010 may apply zero run-length coding to the input residual attribute values.

According to an embodiment of the present disclosure, quantization and zero run-length coding may be performed on the residual attribute values.

According to embodiments, the arithmetic coder 53011 applies arithmetic coding to the prediction modes and residual attribute values output from the residual attribute information quantization processor 53010 and outputs the result as an attribute bitstream.

The geometry bitstream compressed and output by the geometry encoder 51006 and the attribute bitstream compressed and output by the attribute encoder 51007 are output to the transmission processor 51008.

The transmission processor 51008 according to the embodiments may perform an operation and/or transmission method identical or similar to the operation and/or transmission method of the transmission processor 12012 of FIG. 12 , and perform an operation and/or transmission method identical or similar to the operation and/or transmission method of the transmitter 10003 of FIG. 1 . For details, reference will be made to the description of FIG. 1 or 12 .

The transmission processor 51008 according to the embodiments may transmit the geometry bitstream output from the geometry encoder 51006, the attribute bitstream output from the attribute encoder 51007, and the signaling bitstream output from the signaling processor 51005, respectively, or may multiplex the bitstreams into one bitstream to be transmitted.

The transmission processor 51008 according to the embodiments may encapsulate the bitstream into a file or segment (e.g., a streaming segment) and then transmit the encapsulated bitstream over various networks such as a broadcasting network and/or a broadband network.

The signaling processor 51005 according to the embodiments may generate and/or process signaling information and output the same to the transmission processor 51008 in the form of a bitstream. The signaling information generated and/or processed by the signaling processor 51005 will be provided to the geometry encoder 51006, the attribute encoder 51007, and/or the transmission processor 51008 for geometry encoding, attribute encoding, and transmission processing. Alternatively, the signaling processor 51005 may receive signaling information generated by the geometry encoder 51006, the attribute encoder 51007, and/or the transmission processor 51008.

In the present disclosure, the signaling information may be signaled and transmitted on a per parameter set (sequence parameter set (SPS), geometry parameter set (GPS), attribute parameter set (APS), tile parameter set (TPS), or the like) basis. Also, it may be signaled and transmitted on the basis of a coding unit of each image, such as slice or tile. In the present disclosure, signaling information may include metadata (e.g., set values) related to point cloud data, and may be provided to the geometry encoder 51006, the attribute encoder 51007, and/or the transmission processor 51008 for geometry encoding, attribute encoding, and transmission processing. Depending on the application, the signaling information may also be defined at the system side, such as a file format, dynamic adaptive streaming over HTTP (DASH), or MPEG media transport (MMT), or at the wired interface side, such as high definition multimedia interface (HDMI), Display Port, Video Electronics Standards Association (VESA), or CTA.

A method/device according to the embodiments may signal related information to add/perform an operation of the embodiments. The signaling information according to the embodiments may be used in a transmission device and/or a reception device.

According to an embodiment of the present disclosure, information on the maximum number of predictors to be used for attribute prediction (lifting_max_num_direct_predictors), threshold information for enabling adaptive prediction of an attribute (lifting_adaptive_prediction_threshold), neighbor point selection-related option information, and the like may be signaled in at least one of a sequence parameter set, an attribute parameter set, a tile parameter set, or an attribute slice header. In addition, according to an embodiment, predictor index information (predIndex) indicating a prediction mode corresponding to a predictor candidate selected from among a plurality of predictor candidates may be signaled in attribute slice data.

According to embodiments, the neighbor point selection-related option information may include at least one of information about a base neighbor point distance calculation method (e.g., nn_base_distance_calculation_method_type), base neighbor point distance information (e.g., nn_base_distance), maximum neighbor point range information (e.g., nearest_neighbor_max_range), minimum neighbor point range information (e.g. nearest_neighbor_min_range), information about a method of applying the maximum neighbor point distance (e.g., nn_range_filtering_location_type), information about whether to automatically calculate the maximum neighbor point range (e.g. automatic_nn_range_calculation_flag), information about a method of calculating the maximum neighbor point range (e.g., automatic_nn_range_method_type), or information related to the value of Kn (e.g., automatic_max_nn_range_in_table, automatic_nn_range_table_k). According to embodiments, the neighbor point selection-related option information may further include at least one of information about the maximum number of points that may be set as neighbor points (e.g., lifting_num_pred_nearest_neighbours), search range-related information (e.g., lifting_search_range), and/or an LOD configuration method.

Similar to the point cloud video encoder of the transmission device described above, the point cloud video decoder of the reception device performs the same or similar process of generating an LOD₁ set, finding the nearest neighbor points based on the LOD₁ set and registering the same in the predictor as a neighbor point set, calculating a weight based on a distance from each neighbor point, and performing normalization with the weight. Then, the decoder decodes a received prediction mode, and predicts an attribute value of the point according to the decoded prediction mode. In addition, after the received residual attribute value is decoded, the decoded residual attribute value may be added to the predicted attribute value to restore the attribute value of the point.

FIG. 30 is a diagram showing another exemplary point cloud reception device according to embodiments.

The point cloud reception device according to the embodiments may include a reception processor 61001, a signaling processor 61002, a geometry decoder 61003, an attribute decoder 61004, and a post-processor 61005. According to embodiments, the geometry decoder 61003 and the attribute decoder 61004 may be referred to as a point cloud video decoder. According to embodiments, the point cloud video decoder may be referred to as a PCC decoder, a PCC decoding unit, a point cloud decoder, a point cloud decoding unit, or the like.

The reception processor 61001 according to the embodiments may receive a single bitstream, or may receive a geometry bitstream, an attribute bitstream, and a signaling bitstream, respectively. When a file and/or segment is received, the reception processor 61001 according to the embodiments may decapsulate the received file and/or segment and output the decapsulated file and/or segment as a bitstream.

When the single bitstream is received (or decapsulated), the reception processor 61001 according to the embodiments may demultiplex the geometry bitstream, the attribute bitstream, and/or the signaling bitstream from the single bitstream. The reception processor 61001 may output the demultiplexed signaling bitstream to the signaling processor 61002, the geometry bitstream to the geometry decoder 61003, and the attribute bitstream to the attribute decoder 61004.

When the geometry bitstream, the attribute bitstream, and/or the signaling bitstream are received (or decapsulated), respectively, the reception processor 61001 according to the embodiments may deliver the signaling bitstream to the signaling processor 61002, the geometry bitstream to the geometry decoder 61003, and the attribute bitstream to the attribute decoder 61004.

The signaling processor 61002 may parse signaling information, for example, information contained in the SPS, GPS, APS, TPS, metadata, or the like from the input signaling bitstream, process the parsed information, and provide the processed information to the geometry decoder 61003, the attribute decoder 61004, and the post-processor 61005. In another embodiment, signaling information contained in the geometry slice header and/or the attribute slice header may also be parsed by the signaling processor 61002 before decoding of the corresponding slice data. That is, when the point cloud data is partitioned into tiles and/or slices at the transmitting side as shown in FIGS. 16A to 16C, the TPS includes the number of slices included in each tile, and accordingly the point cloud video decoder according to the embodiments may check the number of slices and quickly parse the information for parallel decoding.

Accordingly, the point cloud video decoder according to the present disclosure may quickly parse a bitstream containing point cloud data as it receives an SPS having a reduced amount of data. The reception device may decode tiles upon receiving the tiles, and may decode each slice based on the GPS and APS included in each tile. Thereby, decoding efficiency may be maximized.

That is, the geometry decoder 61003 may reconstruct the geometry by performing the reverse process of the operation of the geometry encoder 51006 of FIG. 15 on the compressed geometry bitstream based on signaling information (e.g., geometry related parameters). The geometry restored (or reconstructed) by the geometry decoder 61003 is provided to the attribute decoder 61004. The attribute decoder 61004 may restore the attribute by performing the reverse process of the operation of the attribute encoder 51007 of FIG. 15 on the compressed attribute bitstream based on signaling information (e.g., attribute related parameters) and the reconstructed geometry. According to embodiments, when the point cloud data is partitioned into tiles and/or slices at the transmitting side as shown in FIGS. 16A to 16C, the geometry decoder 61003 and the attribute decoder 61004 perform geometry decoding and attribute decoding on a tile-by-tile basis and/or slice-by-slice basis.

FIG. 31 is a detailed block diagram illustrating another example of the geometry decoder 61003 and the attribute decoder 61004 according to embodiments.

The arithmetic decoder 63001, the octree reconstruction unit 63002, the geometry information prediction unit 63003, the inverse quantization processor 63004, and the coordinates inverse transformation unit 63005 included in the geometry decoder 61003 of FIG. 31 may perform some or all of the operations of the arithmetic decoder 11000, the octree synthesis unit 11001, the surface approximation synthesis unit 11002, the geometry reconstruction unit 11003, and the coordinates inverse transformation unit 11004 of FIG. 11 , or may perform some or all of the operations of the arithmetic decoder 13002, the occupancy code-based octree reconstruction processor 13003, the surface model processor 13004, and the inverse quantization processor 13005 of FIG. 13 . The positions restored by the geometry decoder 61003 are output to the post-processor 61005.

According to embodiments, when information on the maximum number of predictors to be used for attribute prediction (lifting_max_num_direct_predictors), threshold information for enabling adaptive prediction of an attribute (lifting_adaptive_prediction_threshold), neighbor point selection-related information, and the like are signaled in at least one of a sequence parameter set (SPS), an attribute parameter set (APS), a tile parameter set (TPS), or an attribute slice header, they may be acquired and provided to the attribute decoder 61004 by the signaling processor 61002, or may be acquired directly by the attribute decoder 61004.

The attribute decoder 61004 according to the embodiments may include an arithmetic decoder 63006, an LOD configuration unit 63007, a neighbor point configuration unit 63008, an attribute information prediction unit 63009, and a residual attribute information inverse quantization processor 63010, and an inverse color transformation processor 63011.

The arithmetic decoder 63006 according to the embodiments may arithmetically decode the input attribute bitstream. The arithmetic decoder 63006 may decode the attribute bitstream based on the reconstructed geometry. The arithmetic decoder 63006 performs an operation and/or decoding identical or similar to the operation and/or decoding of the arithmetic decoder 11005 of FIG. 11 or the arithmetic decoder 13007 of FIG. 13 .

According to embodiments, the attribute bitstream output from the arithmetic decoder 63006 may be decoded by one or a combination of two or more of RAHT decoding, LOD-based predictive transform decoding, and lifting transform decoding based on the reconstructed geometry information.

It has been described as an embodiment that the transmission device performs attribute compression by one or a combination of the LOD-based predictive transform coding and the lifting transform coding. Accordingly, an embodiment in which the reception device performs attribute decoding by one or a combination of the LOD-based predictive transform decoding and the lifting transform decoding will be described. The description of the RAHT decoding for the reception device will be omitted.

According to an embodiment, an attribute bitstream that is arithmetically decoded by the arithmetic decoder 63006 is provided to the LOD configuration unit 63007. According to embodiments, the attribute bitstream provided from the arithmetic decoder 63006 to the LOD configuration unit 63007 may contain prediction modes and residual attribute values.

The LOD configuration unit 63007 according to the embodiments generates one or more LODs in the same or similar manner as the LOD configuration unit 53007 of the transmission device, and outputs the generated one or more LODs to the neighbor point configuration unit 63008.

According to embodiments, the LOD configuration unit 63007 may configure one or more LODs using one or more LOD generation methods (or LOD configuration methods). According to embodiments, the LOD generation method used in the LOD configuration unit 63007 may be provided through the signaling processor 61002. For example, the LOD generation method may be signaled in an APS of signaling information. According to embodiments, the LOD generation method may be classified into an octree-based LOD generation method, a distance-based LOD generation method, and a sampling-based LOD generation method.

According to embodiments, a group having different LODs is referred to as an LOD₁ set. Here, 1 represents an LOD as an integer starting from 0. LOD₀ is a set consisting of points having the largest distance therebetween. As 1 increases, the distance between points belonging to LOD₁ decreases.

According to embodiments, prediction modes and residual attribute values, encoded by the transmission device, may be provided for each LODs or only for a leaf node.

In one embodiment, when the LOD₁ set is generated by the LOD configuration unit 63007, the neighbor point set configuration unit 63008 may search for neighbor points equal to or less than X (e.g., 3) points in a group having the same or lower LOD (i.e., a large distance between nodes) based on the LOD₁ set and register the searched neighbor points as a neighbor point set in the predictor.

According to an embodiment, the neighbor point set configuration unit 63008 configures the neighbor point set by obtaining a search range and/or a maximum neighbor point distance based on the signaling information and applying the search range and/or the maximum neighbor point distance to a neighbor point search process.

The neighbor point set configuration unit 63008 according to embodiments may obtain the maximum neighbor point distance by multiplying a base neighbor point distance by NN_range. NN_range is a range within which a neighbor point may be selected and will be referred to as a maximum range within which a neighbor point may be selected, a maximum neighbor point range, a neighbor point range, or a nearest neighbor range. The neighbor point set configuration unit 63008 according to embodiments may calculate/configure the base neighbor point distance by combining one or more of an octree-based method, a distance-based method, a sampling-based method, a Morton code average difference-based method for each LOD, and an average distance difference-based method for each LOD based on the signaling information.

Since a detailed description of calculating/configuring the base neighbor point distance by combining one or more of the octree-based method, the distance-based method, the sampling-based method, the Morton code average difference-based method for each LOD, and the average distance difference-based method for each LOD in the neighbor point set configuration unit 63008 according to embodiments has been given in detail in the above-described process of encoding an attribute of the transmission device, details thereof will be omitted herein.

According to embodiments, the neighbor point set configurator 63008 may acquire a base neighbor point distance from the neighbor point selection-related option information included in the signaling information.

According to embodiments, the neighbor point set configurator 63008 may automatically or manually set the NN_range according to the characteristics of the content. The neighbor point set configurator 63008 may automatically or manually set the NN_range according to the characteristics of the content based on the neighbor point selection-related option information included in the signaling information.

According to embodiments, the neighbor point set configurator 63008 may directly acquire the maximum neighbor point range (NN_range) from the neighbor point selection-related option information, or may calculate the NN_range based on the neighbor point selection-related option information.

Details of the automatic calculation of the NN_range by the neighbor point set configurator 63008 according to the embodiments have been described above in describing the attribute encoding process of the transmission device, and thus description thereof will be skipped.

According to embodiments, the neighbor point selection-related option information may include at least one of information about a base neighbor point distance calculation method (e.g., nn_base_distance_calculation_method_type), base neighbor point distance information (e.g., nn_base_distance), maximum neighbor point range information (e.g., nearest_neighbor_max_range), minimum neighbor point range information (e.g. nearest_neighbor_min_range), information about a method of applying the maximum neighbor point distance (e.g., nn_range_filtering_location_type), information about whether to automatically calculate the maximum neighbor point range (e.g. automatic_nn_range_calculation_flag), information about a method of calculating the maximum neighbor point range (e.g., automatic_nn_range_method_type), or information related to the value of Kn (e.g., automatic_max_nn_range_in_table, automatic_nn_range_table_k). According to embodiments, the neighbor point selection-related option information may further include information about the maximum number of points that may be set as neighbor points (e.g., lifting_num_pred_nearest_neighbours), search range related information (e.g., lifting_search_range), and/or an LOD configuration method. In the present disclosure, for simplicity, at least one of information about the base neighbor point distance calculation method (e.g., nn_base_distance_calculation_method_type) and the base neighbor point distance information (e.g., nn_base_distance) may be referred to as base neighbor point distance related information.

According to embodiments, the information about the base neighbor point distance calculation method (e.g., nn_base_distance_calculation_method_type) may indicate use of a base distance, octree-based maximum neighbor point distance calculation, distance-based maximum neighbor point distance calculation, sampling-based maximum neighbor point distance calculation, maximum neighbor point distance calculation through calculation of the average difference in Morton code between LODs, or maximum neighbor point distance calculation through calculation of the average distance difference between LODs, which is input as a user parameter (or encoder option).

According to embodiments, the information about the method of applying the maximum neighbor point distance (e.g., nn_range_filtering_location_type) may indicate a method by which a distance between points is calculated and a point outside the maximum neighbor point distance is not selected in selecting neighbor points, or a method by which all neighbor points are registered by calculating a distance between the points, and points beyond the maximum neighbor point distance are removed among the registered points.

According to embodiments, information about whether to automatically calculate the maximum neighbor point range (e.g. automatic_nn_range_calculation_flag) may indicate whether to automatically calculate the maximum neighbor point range.

According to embodiments, the information about the method of calculating the maximum neighbor point range (e.g., automatic_nn_range_method_type) may indicate a method of calculating the maximum neighbor point range by estimating the density based on the diagonal length of the bounding box, or a method of calculating the maximum neighbor point range by estimating the density based on the axis length of the bounding box and the number of points.

The method of calculating the maximum neighbor point range by estimating the density based on the diagonal length of the bounding box may include estimating the density using the diagonal length of the bounding box as a denominator, and estimating the density using the diagonal length of the bounding box as a numerator.

The method of calculating the maximum neighbor point range by estimating the density based on the axis length of the bounding box and the number of points may include a method of estimating the density based on the maximum axis length of the bounding box and the number of points, a method of estimating the density based on the minimum axis length of the bounding box and the number of points, and a method of estimating the density based on the middle axis length and the number of points.

According to embodiments, the neighbor point set configurator 63008 estimate the density for automatic calculation, using one or a combination of two or more of the method of estimating the density using the diagonal length of the bounding box as a denominator, the method of estimating the density using the diagonal length of the bounding box as a numerator, the method of estimating the density based on the maximum axis length of the bounding box and the number of points, the method of estimating the density based on the minimum axis length of the bounding box and the number of points, and the method of estimating the density based on the middle axis length and the number of points.

The information related to the value of Kn may include the number of entries in the table of values of Kn (e.g., automatic_max_nn_range_in_table) and a Kn value (e.g., automatic_nn_range_table_k).

According to embodiments, the neighbor point set configurator 63008 may automatically calculate the maximum neighbor point range (NN_range) according to the information about whether to automatically calculate the maximum neighbor point range (e.g., automatic_nn_range_calculation_flag). For example, when the information about whether to automatically calculate the maximum range (e.g., automatic_nn_range_calculation_flag) indicates automatic calculation, the maximum neighbor point range (NN_range) may be automatically calculated based on the information related to the base neighbor point distance, the information about the maximum neighbor point range calculation method, and the information related to the value of Kn.

According to an embodiment, if the maximum neighbor point distance is determined as described above, the neighbor point set configuration unit 63008 searches for X (e.g., 3) NN points among points within the search range in a group having the same or lower LOD (i.e., a large distance between nodes) based on the LOD₁ set as in FIG. 28 . Then the neighbor point set configuration unit 63008 may register only NN points within the maximum neighbor point distance among the X (e.g., 3) NN points as a neighbor point set. Therefore, the number of NN points registered as the neighbor point set is equal to or smaller than X. In other words, NN points that are not within the maximum neighbor point distance among the X NN points are not registered as the neighbor point set and are excluded from the neighbor point set. For example, if two of the three NN points are not within the maximum neighbor point distance, the two NN points are excluded and only the other NN point, i.e., one NN point, is registered as the neighbor point set.

According to another embodiment, if the maximum neighbor point distance is determined as described above, the neighbor point set configuration unit 53008 may search for X (e.g., 3) NN points within the maximum neighbor point distance among points within the search range in a group having the same or lower LOD (i.e., a large distance between nodes) based on the LOD₁ set as in FIG. 29 and register the X NN points as the neighbor point set.

That is, the number of NN points that may be registered as the neighbor point set may vary according to a timing (or position) of applying the maximum neighbor point distance. In other words, the number of NN points registered as the neighbor point set may differ according to whether the maximum neighbor point distance is applied after searching for X NN points through neighbor point search or the maximum neighbor point distance is applied when calculating a distance between points as in FIG. 29 .

Referring to FIG. 28 as an example, the neighbor point set configuration unit 63008 compares the distance values between points within the actual search range and the point Px to search for X NN points and registers only points within the maximum neighbor point distance at an LOD to which the point Px belongs among the X points as the neighbor point set of the point Px. That is, the neighbor points registered as the neighbor point set of the point Px are limited to points within the maximum neighbor point distance at the LOD to which the point Px belongs among the X points.

Referring to FIG. 29 as an example, when comparing the distance values between the points within the actual search range and the point Px, the neighbor point set configuration unit 63008 selects X (e.g., 3) NN points within the maximum neighbor point distance at an LOD to which the point Px belongs from among points in the actual search range and registers the selected points as the neighbor point set of the point Px. That is, neighbor points registered as the neighbor point set of the point Px are limited to points within the maximum neighbor point distance at the LOD to which the point Px belongs.

In FIGS. 28 and 29 , the actual search range may be a value obtained by multiplying the value of the lifting_search_range field by 2 and then adding a center point to the resultant value (i.e., (value of the lifting_search_range field*2)+center point), a value obtained by adding the center value to the value of the lifting_search_range field (i.e., value of lifting_search_range field+center point), or the value of the lifting_search_range field. In an embodiment, the neighbor point set configuration unit 63008 searches for neighbor points of the point Px in the retained list when the number of LODs is plural and searches for neighbor points of the point Px in the index list when the number of LODs is one.

For example, if the number of LODs is 2 or more and information related to the search range (e.g., lifting_search_range field) is 128, the actual search range includes 128 points before the center point Pi, 128 points after the center point Pi, and the center point Pi in the retained list arranged with Morton codes. As another example, if the number of LODs is 1 and the information related to the search range is 128, the actual search range includes 128 points before the center point Pi and the center point Pi in the index list arranged with Morton codes. As another example, if the number of LODs is 1 and the information related to the search range is 128, the actual search range includes 128 points before the current point Px in the index list arranged with Morton codes.

As an example, it is assumed that the neighbor point set configuration unit 63008 selects P2 P4 P6 points as neighbor points of a P3 point (i.e., node) belonging to LOD₁ and registers the selected points as the neighbor point set in the predictor of P3 (see FIG. 9 ).

According to embodiments, when the neighbor point set is registered in each predictor of points to be decoded in the neighbor point set configuration unit 63008, the attribute information predicting unit 63009 predicts an attribute value of a corresponding point from one or more neighbor points registered in each predictor.

According to embodiments, the attribute information predictor 63009 performs a process of predicting an attribute value of the point based on a prediction mode of the point. This attribute prediction process is performed on all points or at least some points of reconstructed geometry.

The prediction mode of a specific point according to embodiments may be one of prediction mode 0 to prediction mode 3.

According to embodiments, prediction mode 0 is a mode that calculates a prediction attribute value through a weighted average, prediction mode 1 is a mode that determines an attribute of a first neighbor point as the prediction attribute value, prediction mode 2 is a mode that determines an attribute of a second neighbor point as the prediction attribute value, and prediction mode 3 is a mode that determines an attribute of a third neighbor point as the prediction attribute value.

According to embodiments, when the maximum difference between attribute values of the neighbor points registered in the predictor of the point is less than a preset threshold, the attribute encoder of the transmitting side sets prediction mode 0 as the prediction mode of the point. When the maximum difference is greater than or equal to the preset threshold, the attribute encoder applies the RDO method to a plurality of candidate prediction modes, and sets one of the candidate prediction modes as a prediction mode of the point. In an embodiment, this process is performed for each point.

According to embodiments, a prediction mode (predIndex) of the point selected by applying the RDO method may be signaled in attribute slice data. Accordingly, the prediction mode of the point may be obtained from the attribute slice data.

According to embodiments, the attribute information prediction unit 63009 may predict the attribute value of each point based on the prediction mode of each point that is set as described above.

For example, when it is assumed that the prediction mode of point P3 is prediction mode 0, the average of the values obtained by multiplying the attributes of points P2, P4, and P6, which are neighbor points registered in the predictor of point P3, by a weight (or normalized weight) may be calculated. The calculated average may be determined as the predicted attribute value of the point.

As another example, when it is assumed that the prediction mode of point P3 is prediction mode 1, the attribute value of point P4, which is a neighbor point registered in the predictor of point P3, may be determined as the predicted attribute value of point P3.

As another example, when it is assumed that the prediction mode of point P3 is prediction mode 2, the attribute value of point P6, which is a neighbor point registered in the predictor of point P3, may be determined as the predicted attribute value of point P3.

As another example, when it is assumed that the prediction mode of point P3 is prediction mode 3, the attribute value of point P2, which is a neighbor point registered in the predictor of point P3, may be determined as the predicted attribute value of point P3.

Once the attribute information prediction unit 63009 obtains the predicted attribute value of the point based on the prediction mode of the point, the residual attribute information inverse quantization processor 63010 restores the attribute value of the point by adding the predicted attribute value of the point predicted by the predictor 63009 to the received residual attribute value of the point, and then performs inverse quantization as a reverse process to the quantization process of the transmission device.

In an embodiment, in the case where the transmitting side applies zero run-length coding to the residual attribute values of points, the residual attribute information inverse quantization processor 63010 performs zero run-length decoding on the residual attribute values of the points, and then performs inverse quantization.

The attribute values restored by the residual attribute information inverse quantization processor 63010 are output to the inverse color transformation processor 63011.

The inverse color transformation processor 63011 performs inverse transform coding for inverse transformation of the color values (or textures) included in the restored attribute values, and then outputs the attributes to the post-processor 61005. The inverse color transformation processor 63011 performs an operation and/or inverse transform coding identical or similar to the operation and/or inverse transform coding of the inverse color transformation unit 11010 of FIG. 11 or the inverse color transformation processor 13010 of FIG. 13 .

The post-processor 61005 may reconstruct point cloud data by matching the positions restored and output by the geometry decoder 61003 with the attributes restored and output by the attribute decoder 61004. In addition, when the reconstructed point cloud data is in a tile and/or slice unit, the post-processor 61005 may perform a reverse process to the spatial partitioning of the transmitting side based on the signaling information. For example, when the bounding box shown in FIG. 16A is partitioned into tiles and slices as shown in of FIG. 16B and FIG. 16C, the tiles and/or slices may be combined based on the signaling information to restore the bounding box as shown in FIG. 16A.

FIG. 32 illustrates an example of a bitstream structure of point cloud data for transmission/reception according to embodiments.

Related information may be signaled to add/perform the embodiments described above. The signaling information according to embodiments may be used in the point cloud video encoder of a transmission end or in the point cloud video decoder of a reception end.

The point cloud video encoder according to embodiments may generate a bitstream as illustrated in FIG. 32 by encoding the geometry information and the attribute information as described above. In addition, signaling information about the point cloud data may be generated and processed by at least one of the geometry encoder, the attribute encoder, or the signaling processor of the point cloud video encoder and may be included in a bitstream.

The signaling information according to embodiments may be received/obtained by at least one of the geometry decoder, the attribute decoder, and the signaling processor of the point cloud video decoder.

The bitstream according to embodiments may be divided into a geometry bitstream, an attribute bitstream, and a signaling bitstream to be transmitted/received or may be combined into one bitstream and transmitted/received.

When a geometry bitstream, an attribute bitstream, and a signaling bitstream according to embodiments are configured as one bitstream, the bitstream may include one or more sub-bitstreams. The bitstream according to the embodiments may include a sequence parameter set (SPS) for sequence level signaling, a geometry parameter set (GPS) for signaling of geometry information coding, one or more attribute parameter sets (APSs) (APS₀, APS₁) for signaling of attribute information coding, a tile parameter set (TPS) for tile level signaling, and one or more slices (slice 0 to slice n). That is, a bitstream of point cloud data according to embodiments may include one or more tiles, and each of the tiles may be a group of slices including one or more slices (slice 0 to slice n). The TPS according to the embodiments may contain information about each of the one or more tiles (e.g., coordinate value information and height/size information about the bounding box). Each slice may include one geometry bitstream (Geom0) and one or more attribute bitstreams (Attr0 and Attr1). For example, a first slice (slice 0) may include one geometry bitstream (Geom0⁰) and one or more attribute bitstreams (Attr0⁰, Attr1⁰).

The geometry bitstream (or geometry slice) in each slice may be composed of a geometry slice header (geom_slice_header) and geometry slice data (geom_slice_data). According to embodiments, geom_slice_header may include identification information (geom_parameter_set_id), a tile identifier (geom_tile_id), and a slice identifier (geom_slice_id) for a parameter set included in the GPS, and information (geomBoxOrigin, geom_box_log2_scale, geom_max_node_size_log2,_geom_num_points) about data contained in the geometry slice data (geom_slice_data). geomBoxOrigin is geometry box origin information indicating the origin of the box of the geometry slice data, geom_box_log2_scale is information indicating the log scale of the geometry slice data, geom_max_node_size_log2 is information indicating the size of the root geometry octree node, and geom_num_points is information related to the number of points of the geometry slice data. According to embodiments, the geom_slice_data may include geometry information (or geometry data) about the point cloud data in a corresponding slice.

Each attribute bitstream (or attribute slice) in each slice may be composed of an attribute slice header (attr_slice_header) and attribute slice data (attr_slice_data). According to embodiments, the attr_slice_header may include information about the corresponding attribute slice data. The attribute slice data may contain attribute information (or attribute data or attribute value) about the point cloud data in the corresponding slice. When there is a plurality of attribute bitstreams in one slice, each of the bitstreams may contain different attribute information. For example, one attribute bitstream may contain attribute information corresponding to color, and another attribute stream may contain attribute information corresponding to reflectance.

FIG. 33 shows an exemplary bitstream structure for point cloud data according to embodiments.

FIG. 34 illustrates a connection relationship between components in a bitstream of point cloud data according to embodiments.

The bitstream structure for the point cloud data illustrated in FIGS. 33 and 34 may represent the bitstream structure for point cloud data shown in FIG. 32 .

According to the embodiments, the SPS may include an identifier (seq_parameter_set_id) for identifying the SPS, and the GPS may include an identifier (geom_parameter_set_id) for identifying the GPS and an identifier (seq_parameter_set_id) indicating an active SPS to which the GPS belongs. The APS may include an identifier (attr_parameter_set_id) for identifying the APS and an identifier (seq_parameter_set_id) indicating an active SPS to which the APS belongs.

According to embodiments, a geometry bitstream (or geometry slice) may include a geometry slice header and geometry slice data. The geometry slice header may include an identifier (geom_parameter_set_id) of an active GPS to be referred to by a corresponding geometry slice. Moreover, the geometry slice header may further include an identifier (geom_slice_id) for identifying a corresponding geometry slice and/or an identifier (geom_tile_id) for identifying a corresponding tile. The geometry slice data may include geometry information belonging to a corresponding slice.

According to embodiments, an attribute bitstream (or attribute slice) may include an attribute slice header and attribute slice data. The attribute slice header may include an identifier (attr_parameter_set_id) of an active APS to be referred to by a corresponding attribute slice and an identifier (geom_slice_id) for identifying a geometry slice related to the attribute slice. The attribute slice data may include attribute information belonging to a corresponding slice.

That is, the geometry slice refers to the GPS, and the GPS refers the SPS. In addition, the SPS lists available attributes, assigns an identifier to each of the attributes, and identifies a decoding method. The attribute slice is mapped to output attributes according to the identifier. The attribute slice has a dependency on the preceding (decoded) geometry slice and the APS. The APS refers to the SPS.

According to embodiments, parameters necessary for encoding of the point cloud data may be newly defined in a parameter set of the point cloud data and/or a corresponding slice header. For example, when encoding of the attribute information is performed, the parameters may be added to the APS. When tile-based encoding is performed, the parameters may be added to the tile and/or slice header.

As shown in FIGS. 32, 33, and 34 , the present disclosure provides tiles or slices such that the point cloud data may be partitioned and processed by regions. According to embodiments, the respective regions of the bitstream may have different importance. Accordingly, when the point cloud data is partitioned into tiles, a different filter (encoding method) and a different filter unit may be applied to each tile. When the point cloud data is partitioned into slices, a different filter and a different filter unit may be applied to each slice.

When the point cloud data is partitioned and compressed, the transmission device and the reception device according to the embodiments may transmit and receive a bitstream in a high-level syntax structure for selective transmission of attribute information in the partitioned regions.

The transmission device according to the embodiments may transmit point cloud data according to the bitstream structure as shown in FIGS. 32, 33, and 34 . Accordingly, a method to apply different encoding operations and use a good-quality encoding method for an important region may be provided. In addition, efficient encoding and transmission may be supported according to the characteristics of point cloud data, and attribute values may be provided according to user requirements.

The reception device according to the embodiments may receive the point cloud data according to the bitstream structure as shown in FIGS. 32, 33, and 34 . Accordingly, different filtering (decoding) methods may be applied to the respective regions (regions partitioned into tiles or into slices), rather than a complexly decoding (filtering) method being applied to the entire point cloud data. Therefore, better image quality in a region important is provided to the user and an appropriate latency to the system may be ensured.

As described above, a tile or a slice is provided to process the point cloud data by partitioning the point cloud data by region. In partitioning the point cloud data by region, an option to generate a different set of neighbor points for each region may be set. Thereby, a selection method having low complexity and slightly lower reliability, or a selection method having high complexity and high reliability may be provided.

Neighbor point selection-related option information for a sequence required in a process of encoding/decoding attribute information according to embodiments may be signaled in an SPS and/or an APS.

According to embodiments, if a tile or slice having different attribute characteristics is present in the same sequence, the neighbor point selection-related option information for the sequence may be signaled in a TPS and/or an attribute slice header for each slice.

According to embodiments, when the point cloud data is divided by regions, attribute characteristics of a specific region may be different from attribute characteristics of the sequence and thus may be differently configured through a different maximum neighbor point range configuration function.

Therefore, when the point cloud data is divided by tiles, a different maximum neighbor point range may be applied to each tile. In addition, when the point cloud data is divided by slices, a different maximum neighbor point range may be applied to each slice.

At least one of the SPS, the APS, the TPS, and the attribute slice header for each slice according to embodiments may include neighbor point selection-related option information. According to embodiments, the neighbor point selection-related option information may include information related to the maximum neighbor point range.

According to embodiments, the neighbor point selection-related option information may include at least one of information about a base neighbor point distance calculation method (e.g., nn_base_distance_calculation_method_type), base neighbor point distance information (e.g., nn_base_distance), maximum neighbor point range information (e.g., nearest_neighbor_max_range), minimum neighbor point range information (e.g. nearest_neighbor_min_range), information about a method of applying the maximum neighbor point distance (e.g., nn_range_filtering_location_type), information about whether to automatically calculate the maximum neighbor point range (e.g. automatic_nn_range_calculation_flag), information about a method of calculating the maximum neighbor point range (e.g., automatic_nn_range_method_type), or information related to the value of Kn (e.g., automatic_max_nn_range_in_table, automatic_nn_range_table_k).

According to embodiments, the neighbor point selection-related option information may further include information about the maximum number of points that may be set as neighbor points (e.g., lifting_num_pred_nearest_neighbours), search range-related information (e.g., lifting_search_range), and/or an LOD configuration method.

A field, which is the term used in syntaxes of the present disclosure described later, may have the same meaning as a parameter or an element.

FIG. 35 shows an embodiment of a syntax structure of a sequence parameter set (SPS) (seq_parameter_set_rbsp( )) according to the present disclosure. The SPS may include sequence information about a point cloud data bitstream. In particular, in this example, the SPS includes neighbor point selection-related option information.

The SPS according to the embodiments may include a profile_idc field, a profile_compatibility_flags field, a level_idc field, an sps_bounding_box_present_flag field, an sps_source_scale_factor field, an sps_seq_parameter_set_id field, an sps_num_attribute_sets field, and an sps_extension_present_flag field.

The profile_idc field indicates a profile to which the bitstream conforms.

The profile_compatibility_flags field equal to 1 may indicate that the bitstream conforms to the profile indicated by profile_idc.

The level_idc field indicates a level to which the bitstream conforms.

The sps_bounding_box_present_flag field indicates whether source bounding box information is signaled in the SPS. The source bounding box information may include offset and size information about the source bounding box. For example, the sps_bounding_box_present_flag field equal to 1 indicates that the source bounding box information is signaled in the SPS. The sps_bounding_box_present_flag field equal to 0 indicates the source bounding box information is not signaled. The sps_source_scale_factor field indicates the scale factor of the source point cloud.

The sps_seq_parameter_set_id field provides an identifier for the SPS for reference by other syntax elements.

The sps_num_attribute_sets field indicates the number of coded attributes in the bitstream.

The sps_extension_present_flag field specifies whether the sps_extension_data syntax structure is present in the SPS syntax structure. For example, the sps_extension_present_flag field equal to 1 specifies that the sps_extension_data syntax structure is present in the SPS syntax structure. The sps_extension_present_flag field equal to 0 specifies that this syntax structure is not present. When not present, the value of the sps_extension_present_flag field is inferred to be equal to 0.

When the sps_bounding_box_present_flag field is equal to 1, the SPS according to embodiments may further include an sps_bounding_box_offset_x field, an sps_bounding_box_offset_y field, an sps_bounding_box_offset_z field, an sps_bounding_box_scale_factor field, an sps_bounding_box_size_width field, an sps_bounding_box_size_height field, and an sps_bounding_box_size_depth field.

The sps_bounding_box_offset_x field indicates the x offset of the source bounding box in the Cartesian coordinates. When the x offset of the source bounding box is not present, the value of sps_bounding_box_offset_x is 0.

The sps_bounding_box_offset_y field indicates the y offset of the source bounding box in the Cartesian coordinates. When the y offset of the source bounding box is not present, the value of sps_bounding_box_offset_y is 0.

The sps_bounding_box_offset_z field indicates the z offset of the source bounding box in the Cartesian coordinates. When the z offset of the source bounding box is not present, the value of sps_bounding_box_offset_z is 0.

The sps_bounding_box_scale_factor field indicates the scale factor of the source bounding box in the Cartesian coordinates. When the scale factor of the source bounding box is not present, the value of sps_bounding_box_scale_factor may be 1.

The sps_bounding_box_size_width field indicates the width of the source bounding box in the Cartesian coordinates. When the width of the source bounding box is not present, the value of the sps_bounding_box_size_width field may be 1.

The sps_bounding_box_size_height field indicates the height of the source bounding box in the Cartesian coordinates. When the height of the source bounding box is not present, the value of the sps_bounding_box_size_height field may be 1.

The sps_bounding_box_size_depth field indicates the depth of the source bounding box in the Cartesian coordinates. When the depth of the source bounding box is not present, the value of the sps_bounding_box_size_depth field may be 1.

The SPS according to embodiments includes an iteration statement repeated as many times as the value of the sps_num_attribute_sets field. In an embodiment, i is initialized to 0, and is incremented by 1 each time the iteration statement is executed. The iteration statement is repeated until the value of i becomes equal to the value of the sps_num_attribute_sets field. The iteration statement may include an attribute_dimension[i] field, an attribute_instance_id[i] field, an attribute_bitdepth[i] field, an attribute_cicp_colour_primaries[i] field, an attribute_cicp_transfer_characteristics[i] field, an attribute_cicp_matrix_coeffs[i] field, an attribute_cicp_video_full_range_flag[i] field, and a known_attribute_label_flag[i] field.

The attribute_dimension[i] field specifies the number of components of the i-th attribute.

The attribute_instance_id[i] field specifies the instance ID of the i-th attribute.

The attribute_bitdepth[i] field specifies the bitdepth of the i-th attribute signal(s).

The attribute_cicp_colour_primaries[i] field indicates chromaticity coordinates of the color attribute source primaries of the i-th attribute.

The attribute_cicp_transfer_characteristics[i] field either indicates the reference opto-electronic transfer characteristic function of the colour attribute as a function of a source input linear optical intensity with a nominal real-valued range of 0 to 1 or indicates the inverse of the reference electro-optical transfer characteristic function as a function of an output linear optical intensity.

The attribute_cicp_matrix_coeffs[i] field describes the matrix coefficients used in deriving luma and chroma signals from the green, blue, and red, or Y, Z, and X primaries.

The attribute_cicp_video_full_range_flag[i] field indicates the black level and range of the luma and chroma signals as derived from E′Y, E′PB, and E′PR or E′R, E′G, and E′B real-valued component signals.

The known_attribute_label_flag[i] field specifies whether a known_attribute_label field or an attribute_label_four_bytes field is signaled for the i-th attribute. For example, the value of the known_attribute_label_flag[i] field equal to 0 specifies that the known_attribute_label field is signaled for the i-th attribute. The known_attribute_label_flag[i] field equal to 1 specifies that the attribute_label_four_bytes field is signaled for the i-th attribute.

The known_attribute_label[i] field may specify an attribute type. For example, the known_attribute_label[i] field equal to 0 may specify that the i-th attribute is color. The known_attribute_label[i] field equal to 1 specifies that the i-th attribute is reflectance. The known_attribute_label[i] field equal to 2 may specify that the i-th attribute is frame index.

The attribute_label_four_bytes field indicates the known attribute type with a 4-byte code.

In this example, the attribute_label_four_bytes field indicates color when equal to 0 and indicates reflectance when is equal to 1.

According to embodiments, when the sps_extension_present_flag field is equal to 1, the SPS may further include a sps_extension_data_flag field.

The sps_extension_data_flag field may have any value.

According to embodiments, the SPS may further include neighbor point selection-related option information as follows.

According to embodiments, the neighbor point selection-related option information may be included in an iteration statement iterated as many times as the value of the sps_num_attribute_sets field described above.

That is, the iteration statement may further include an nn_base_distance_calculation_method_type[i] field, a nearest_neighbour_max_range[i] field, a nearest_neighbour_min_range[i] field, a nn_range_filtering_location_type[i] field, and an automatic_nn_range_calculation_flag[i] field.

The nn_base_distance_calculation_method_type[i] field may indicate a base neighbor point distance calculation method applied in compressing the i-th attribute of a corresponding sequence. For example, the nn_base_distance_calculation_method_type[i] field equal to 0 may indicate use of a base distance. The nn_base_distance_calculation_method_type[i] field equal to 1 may indicate octree-based maximum neighbor point distance calculation. The nn_base_distance_calculation_method_type[i] field equal to 2 may indicate distance-based maximum neighbor point distance calculation. The nn_base_distance_calculation_method_type[i] field equal to 3 may indicate sampling-based maximum neighbor point distance calculation. The nn_base_distance_calculation_method_type[i] field equal to 4 may indicate maximum neighbor point distance calculation through calculation of the average difference in Morton code between LODs. The nn_base_distance_calculation_method_type[i] field equal to 5 may indicate maximum neighbor point distance calculation through calculation of the average distance difference between LODs.

According to embodiments, when the value of the nn_base_distance_calculation_method_type[i] field is 0, that is, the field indicates use of the input base distance, the iteration statement may further include an nn_base_distance[i] field.

The nn_base_distance[i] field may specify a base neighbor point distance applied in compressing the i-th attribute of a corresponding sequence.

The nearest_neighbour_max_range[i] field may indicate the maximum neighbor point range applied in compressing the i-th attribute of the sequence. According to embodiments, the value of the nearest_neighbour_max_range[i] field may be used as a value of NN_range in Equation 5. According to embodiments, the nearest_neighbour_max_range[i] field may be used to limit the distance of a point registered as a neighbor. For example, when LODs are generated based on an octree, the value of the nearest_neighbour_max_range[i] field may be the number of octree nodes around the point.

The nearest_neighbour_min_range[i] field may indicate the minimum neighbor point range applied in compressing the i-th attribute of the sequence.

The nn_range_filtering_location_type[i] field may indicate a method of applying the maximum neighbor point distance in compressing the i-th attribute of the sequence. For example, when the value of the nn_range_filtering_location_type[i] field is 0, it may indicate a method by which a distance between points is calculated and a point outside the maximum neighbor point distance is not selected in selecting neighbor points. As another example, when the value of the nn_range_filtering_location_type[i] field is 1, it may indicate a method by which all neighbor points are registered by calculating a distance between the points, and points beyond the maximum neighbor point distance are removed among the registered points.

The automatic_nn_range_calculation_flag[i] field may indicate whether to automatically calculate the maximum neighbor point range in compressing the i-th attribute of the sequence. For example, when the value of the automatic_nn_range_calculation_flag[i] field is 0 (i.e., TRUE), it may indicate automatic calculation of the maximum neighbor point range.

According to embodiments, when the value of the automatic_nn_range_calculation_flag[i] field is 0, that is, when the field indicates the automatic calculation of the maximum neighbor point range, the iteration statement may further include an automatic_nn_range_method_type[i] field and an automatic_max_nn_range_in_table[i] field.

The automatic_nn_range_method_type[i] field may indicate a method of calculating the maximum neighbor point range in compressing the i-th attribute of the sequence.

For example, the automatic_nn_range_method_type[i] field equal to 1 may indicate the method of estimating the density using the diagonal length of the bounding box as a denominator. The automatic_nn_range_method_type[i] field equal to 2 may indicate the method of estimating the density using the diagonal length of the bounding box as a numerator. The automatic_nn_range_method_type[i] field equal to 3 may indicate the method of estimating the density based on the maximum axis length of the bounding box and the number of points. The automatic_nn_range_method_type[i] field equal to 4 may indicate the method of estimating the density based on the minimum axis length of the bounding box and the number of points. The automatic_nn_range_method_type[i] field equal to 5 may indicate the method of estimating the density based on the middle axis length and the number of points. As another example, the automatic_nn_range_method_type[i] field equal to 6 may indicate a calculation method combining the method of estimating the density using the diagonal length of the bounding box as the denominator and the method of estimating the density based on the maximum axis length of the bounding box and the number of points. The automatic_nn_range_method_type[i] field equal to 7 may indicate a calculation method combining the method of estimating the density using the diagonal length of the bounding box as the denominator and the method of estimating the density based on the minimum axis length of the bounding box and the number of points. The automatic_nn_range_method_type[i] field equal to 8 may indicate a calculation method combining the method of estimating the density using the diagonal length of the bounding box as the denominator and the method of estimating the density based on the middle axis length of the bounding box and the number of points. The automatic_nn_range_method_type[i] field equal to 9 may indicate a calculation method combining the method of estimating the density using the diagonal length of the bounding box as the numerator and the method of estimating the density based on the maximum axis length and the number of points of the bounding box. The automatic_nn_range_method_type[i] field equal to 10 may indicate a calculation method combining the method of estimating the density using the diagonal length of the bounding box as the numerator and the method of estimating the density based on the minimum axis length of the bounding box and the number of points. The automatic_nn_range_method_type[i] field equal to 11 may indicate the method of estimating the density using the diagonal length of the bounding box as the numerator and the method of estimating the density based on the middle axis length of the bounding box and the number of points.

The automatic_max_nn_range_in_table[i] field may indicate the number of entries in the table of values of Kn in compressing the i-th attribute of the sequence.

The SPS according to embodiments may include an iteration statement iterated as many times as the value of the automatic_max_nn_range_in_table[i] field. In this case, according to an embodiment, j is initialized to 0 and is incremented by 1 each time the iteration statement is executed. The iteration statement is iterated until the value of j becomes the value of the automatic_max_nn_range_in_table[i] field. This iteration statement may include an automatic_nn_range_table_k[i][j] field.

The automatic_nn_range_table_k[i][j] field may indicate a value of Kn in compressing the i-th attribute of the corresponding sequence.

FIG. 36 shows an embodiment of a syntax structure of the geometry parameter set (GPS) (geometry_parameter_set( )) according to the present disclosure. The GPS according to the embodiments may contain information on a method of encoding geometry information about point cloud data contained in one or more slices.

According to embodiments, the GPS may include a gps_geom_parameter_set_id field, a gps_seq_parameter_set_id field, a gps_box_present_flag field, a unique geometry_points_flag field, a neighbour_context_restriction_flag field, an inferred_direct_coding_mode_enabled_flag field, a bitwise_occupancy_coding_flag field, an adjacent_child_contextualization_enabled_flag field, a log2_neighbour_avail_boundary field, a log2_intra_pred_max_node_size field, a log2_trisoup_node_size field, and a gps_extension_present_flag field.

The gps_geom_parameter_set_id field provides an identifier for the GPS for reference by other syntax elements.

The gps_seq_parameter_set_id field specifies the value of sps_seq_parameter_set_id for the active SPS.

The gps_box_present_flag field specifies whether additional bounding box information is provided in a geometry slice header that references the current GPS. For example, the gps_box_present_flag field equal to 1 may specify that additional bounding box information is provided in a geometry header that references the current GPS. Accordingly, when the gps_box_present_flag field is equal to 1, the GPS may further include a gps_gsh_box_log2_scale_present_flag field.

The gps_gsh_box_log2_scale_present_flag field specifies whether the gps_gsh_box_log2_scale field is signaled in each geometry slice header that references the current GPS. For example, the gps_gsh_box_log2_scale_present_flag field equal to 1 may specify that the gps_gsh_box_log2_scale field is signaled in each geometry slice header that references the current GPS. As another example, the gps_gsh_box_log2_scale_present_flag field equal to 0 may specify that the gps_gsh_box_log2_scale field is not signaled in each geometry slice header and a common scale for all slices is signaled in the gps_gsh_box_log2_scale field of the current GPS.

When the gps_gsh_box_log2_scale_present_flag field is equal to 0, the GPS may further include a gps_gsh_box_log2_scale field.

The gps_gsh_box_log2_scale field indicates the common scale factor of the bounding box origin for all slices that refer to the current GPS.

The unique geometry_points_flag field indicates whether all output points have unique positions. For example, the unique geometry_points_flag field equal to 1 indicates that all output points have unique positions. The unique geometry_points_flag field equal to 0 indicates that in all slices that refer to the current GPS, the two or more of the output points may have the same position.

The neighbor_context_restriction_flag field indicates contexts used for octree occupancy coding. For example, the neighbour_context_restriction_flag field equal to 0 indicates that octree occupancy coding uses contexts determined from six neighboring parent nodes. The neighbour_context_restriction_flag field equal to 1 indicates that octree occupancy coding uses contexts determined from sibling nodes only.

The inferred_direct_coding_mode_enabled_flag field indicates whether the direct_mode_flag field is present in the geometry node syntax. For example, the inferred_direct_coding_mode_enabled_flag field equal to 1 indicates that the direct_mode_flag field may be present in the geometry node syntax. For example, the inferred_direct_coding_mode_enabled_flag field equal to 0 indicates that the direct_mode_flag field is not present in the geometry node syntax.

The bitwise_occupancy_coding_flag field indicates whether geometry node occupancy is encoded using bitwise contextualization of the syntax element occupancy map. For example, the bitwise_occupancy_coding_flag field equal to 1 indicates that geometry node occupancy is encoded using bitwise contextualisation of the syntax element occupancy_map. For example, the bitwise_occupancy_coding_flag field equal to 0 indicates that geometry node occupancy is encoded using the dictionary encoded syntax element occupancy_byte.

The adjacent_child_contextualization_enabled_flag field indicates whether the adjacent children of neighboring octree nodes are used for bitwise occupancy contextualization. For example, the adjacent_child_contextualization_enabled_flag field equal to 1 indicates that the adjacent children of neighboring octree nodes are used for bitwise occupancy contextualization. For example, adjacent_child_contextualization_enabled_flag equal to 0 indicates that the children of neighbouring octree nodes are not used for the occupancy contextualization.

The log2_neighbour_avail_boundary field specifies the value of the variable NeighbAvailBoundary that is used in the decoding process as follows:

NeighbAvailBoundary=2^(log2_neighbour_avail_boundary)

For example, when the neighbour_context_restriction_flag field is equal to 1, NeighbAvailabilityMask may be set equal to 1. For example, when the neighbour_context_restriction_flag field is equal to 0, NeighbAvailabilityMask may be set equal to 1<<log2_neighbour_avail_boundary.

The log2_intra_pred_max_node_size field specifies the octree node size eligible for occupancy intra prediction.

The log2_trisoup_node_size field specifies the variable TrisoupNodeSize as the size of the triangle nodes as follows.

TrisoupNodeSize=1<<log2_trisoup_node_size

The gps_extension_present_flag field specifies whether the gps_extension_data syntax structure is present in the GPS syntax structure. For example, gps_extension_present_flag equal to 1 specifies that the gps_extension_data syntax structure is present in the GPS syntax. For example, gps_extension_present_flag equal to 0 specifies that this syntax structure is not present in the GPS syntax.

When the value of the gps_extension_present_flag field is equal to 1, the GPS according to the embodiments may further include a gps_extension_data_flag field.

The gps_extension_data_flag field may have any value. Its presence and value do not affect the decoder conformance to profiles.

FIG. 37 shows an embodiment of a syntax structure of the attribute parameter_set (APS) (attribute_parameter_set( )) according to the present disclosure. The APS according to the embodiments may contain information on a method of encoding attribute information in point cloud data contained in one or more slices. According to embodiments, the APS may include neighbor point selection-related option information.

The APS according to the embodiments may include an aps_attr_parameter_set_id field, an aps seq_parameter_set_id field, an attr_coding_type field, an aps_attr_initial_qp field, an aps_attr_chroma_qp_offset field, an aps_slice_qp_delta_present_flag field, and an aps_flag field.

The aps_attr_parameter_set_id field provides an identifier for the APS for reference by other syntax elements.

The aps seq_parameter_set_id field specifies the value of sps_seq_parameter_set_id for the active SPS.

The attr_coding_type field indicates the coding type for the attribute.

In this example, the attr_coding_type field equal to 0 indicates predicting weight lifting (or LOD with predicting transform) as the coding type. The attr_coding_type field equal to 1 indicates RAHT as the coding type. The attr_coding_type field equal to 2 indicates fix weight lifting(or LOD with lifting transform).

The aps_attr_initial_qp field specifies the initial value of the variable SliceQp for each slice referring to the APS. The initial value of SliceQp is modified at the attribute slice segment layer when a non-zero value of slice_qp_delta_luma or slice_qp_delta_luma are decoded

The aps_attr_chroma_qp_offset field specifies the offsets to the initial quantization parameter signaled by the syntax aps_attr_initial_qp.

The aps_slice_qp_delta_present_flag field specifies whether the ash_attr_qp_delta_luma and ash_attr_qp_delta_chroma syntax elements are present in the attribute slice header (ASH). For example, the aps_slice_qp_delta_present_flag field equal to 1 specifies that the ash_attr_qp_delta_luma and ash_attr_qp_delta_chroma syntax elements are present in the ASH. For example, the aps_slice_qp_delta_present_flag field equal to 0 specifies that the ash_attr_qp_delta_luma and ash_attr_qp_delta_chroma syntax elements are not present in the ASH.

When the value of the attr_coding_type field is 0 or 2, that is, the coding type is predicting weight lifting (or LOD with predicting transform) or fix weight lifting (or LOD with lifting transform), the APS according to the embodiments may further include a lifting_num_pred_nearest_neighbours field, a lifting_max_num_direct_predictors a lifting_search_range field, a lifting_lod_regular_sampling_enabled_flag field, a lifting_num_detail_levels_minus1 field.

The lifting_num_pred_nearest_neighbours field specifies the maximum number (i.e., X value) of nearest neighbors to be used for prediction.

The lifting_max_num_direct_predictors field specifies the maximum number of predictors to be used for direct prediction. The value of the variable MaxNumPredictors that is used in the decoding process as follows:

MaxNumPredictors=lifting_max_num_direct_predictors field+1

The lifting_search_range field specifies a search range used to determine nearest neighbors.

The lifting_num_detail_levels_minus1 field specifies the number of levels of detail for the attribute coding.

The lifting_lod_regular_sampling_enabled_flag field specifies whether levels of detail (LOD) are built by using a regular sampling strategy. For example, the lifting_lod_regular_sampling_enabled_flag equal to 1 specifies that levels of detail (LOD) are built by using a regular sampling strategy. The lifting_lod_regular_sampling_enabled_flag equal to 0 specifies that a distance-based sampling strategy is used instead.

The APS according to embodiments includes an iteration statement repeated as many times as the value of the lifting_num_detail_levels_minus1 field. In an embodiment, the index (idx) is initialized to 0 and incremented by 1 every time the iteration statement is executed, and the iteration statement is repeated until the index (idx) is greater than the value of the lifting_num_detail_levels_minus1 field. This iteration statement may include a lifting_sampling_period[idx] field when the value of the lifting_lod_decimation_enabled_flag field is true (e.g., 1), and may include a lifting_sampling_distance_squared[idx] field when the value of the lifting_lod_decimation_enabled_flag field is false (e.g., 0).

The lifting_sampling_period[idx] field specifies the sampling period for the level of detail idx.

The lifting_sampling_distance_squared[idx] field specifies the square of the sampling distance for the level of detail idx.

When the value of the attr_coding_type field is 0, that is, when the coding type is predicting weight lifting (or LOD with predicting transform), the APS according to the embodiments may further include a lifting_adaptive_prediction_threshold field, and a lifting_intra_lod_prediction_num_layers field.

The lifting_adaptive_prediction_threshold field specifies the threshold to enable adaptive prediction.

The lifting_intra_lod_prediction_num_layers field specifies the number of LOD layers where decoded points in the same LOD layer could be referred to generate a prediction value of a target point. For example, the lifting_intra_lod_prediction_num_layers field equal to num_detail_levels_minus1 plus 1 indicates that target point could refer to decoded points in the same LOD layer for all LOD layers. For example, the lifting_intra_lod_prediction_num_layers field equal to 0 indicates that target point could not refer to decoded points in the same LoD layer for any LoD layers.

The aps_extension_present_flag field specifies whether the aps_extension_data syntax structure is present in the APS syntax structure. For example, the aps_extension_present_flag field equal to 1 specifies that the aps_extension_data syntax structure is present in the APS syntax structure. For example, the aps_extension_present_flag field equal to 0 specifies that this syntax structure is not present in the APS syntax structure.

When the value of the aps_extension_present_flag field is 1, the APS according to the embodiments may further include an aps_extension_data_flag field.

The aps_extension_data_flag field may have any value. Its presence and value do not affect decoder conformance to profiles.

The APS according to embodiments may further include neighbor point selection-related option information as follows.

When the value of the attr_coding_type field is 0 or 2, that is, the coding type is “predicting weight lifting (or LOD with predicting transform),” or “fix weight lifting (or LOD with lifting transform),” the APS according to embodiments may further include a different_nn_range_in_tile_flag field and a different_nn_range_per_lod_flag field.

The different_nn_range_in_tile_flag field may specify whether a sequence is using a different maximum/minimum neighbor point range for a partitioned tile from the sequence.

The different_nn_range_per_lod_flag field may specify whether to use a different maximum/minimum neighbor point range for each LOD.

For example, when the value of the different_nn_range_per_lod_flag field is FALSE, the APS may further include a nearest_neighbour_max_range field, a nearest_neighbour_min_range field, an nn_base_distance_calculation_method_type field, an nn_range_filtering_location_type field, and an automatic_nn_range_calculation_flag field.

The nearest_neighbour_max_range field may indicate the maximum neighbor point range in compressing a corresponding attribute. According to embodiments, the nearest_neighbour_max_range field may be used to limit the distance of a point registered as a neighbor. According to embodiments, the value of the nearest_neighbour_max_range field may be used as a value of NN_range in Equation 5.

The nearest_neighbour_min_range field may indicate may indicate the minimum neighbor point range in compressing the attribute.

The nn_base_distance_calculation_method_type field may indicate a base neighbor point distance calculation method applied in compressing the attribute.

For example, the nn_base_distance_calculation_method_type field equal to 0 may indicate use of a base distance. The nn_base_distance_calculation_method_type field equal to 1 may indicate octree-based maximum neighbor point distance calculation. The nn_base_distance_calculation_method_type field equal to 2 may indicate distance-based maximum neighbor point distance calculation. The nn_base_distance_calculation_method_type field equal to 3 may indicate sampling-based maximum neighbor point distance calculation. The nn_base_distance_calculation_method_type field equal to 4 may indicate maximum neighbor point distance calculation through calculation of the average difference in Morton code between LODs. The nn_base_distance_calculation_method_type field equal to 5 may indicate maximum neighbor point distance calculation through calculation of the average distance difference between LODs.

According to embodiments, when the value of the nn_base_distance_calculation_method_type field is 0, that is, the field indicates use of the input base distance, the iteration statement may further include an nn_base_distance field.

The nn_base_distance field may specify a base neighbor point distance applied in compressing the attribute.

The nn_range_filtering_location_type field may indicate a method of applying the maximum neighbor point distance in compressing a corresponding attribute. For example, when the value of the nn_range_filtering_location_type field is 0, it may indicate a method by which a distance between points is calculated and a point outside the maximum neighbor point distance is not selected in selecting neighbor points. As another example, when the value of the nn_range_filtering_location_type field is 1, it may indicate a method by which all neighbor points are registered by calculating a distance between the points, and points beyond the maximum neighbor point distance are removed among the registered points.

The automatic_nn_range_calculation_flag field may indicate whether to automatically calculate the maximum neighbor point range in compressing a corresponding attribute. For example, when the value of the automatic_nn_range_calculation_flag field is 0 (i.e., TRUE), it may indicate automatic calculation of the maximum neighbor point range.

According to embodiments, when the value of the automatic_nn_range_calculation_flag field is 0, that is, when the field indicates the automatic calculation of the maximum neighbor point range, the iteration statement may further include an automatic_nn_range_method_type field and an automatic_max_nn_range_in_table field.

The automatic_nn_range_method_type field may indicate a method of calculating the maximum neighbor point range in compressing a corresponding attribute.

For example, the automatic_nn_range_method_type field equal to 1 may indicate the method of estimating the density using the diagonal length of the bounding box as a denominator. The automatic_nn_range_method_type field equal to 2 may indicate the method of estimating the density using the diagonal length of the bounding box as a numerator. The automatic_nn_range_method_type field equal to 3 may indicate the method of estimating the density based on the maximum axis length of the bounding box and the number of points. The automatic_nn_range_method_type field equal to 4 may indicate the method of estimating the density based on the minimum axis length of the bounding box and the number of points. The automatic_nn_range_method_type field equal to 5 may indicate the method of estimating the density based on the middle axis length and the number of points. As another example, the automatic_nn_range_method_type field equal to 6 may indicate a calculation method combining the method of estimating the density using the diagonal length of the bounding box as the denominator and the method of estimating the density based on the maximum axis length of the bounding box and the number of points. The automatic_nn_range_method_type field equal to 7 may indicate a calculation method combining the method of estimating the density using the diagonal length of the bounding box as the denominator and the method of estimating the density based on the minimum axis length of the bounding box and the number of points. The automatic_nn_range_method_type field equal to 8 may indicate a calculation method combining the method of estimating the density using the diagonal length of the bounding box as the denominator and the method of estimating the density based on the middle axis length of the bounding box and the number of points. The automatic_nn_range_method_type field equal to 9 may indicate a calculation method combining the method of estimating the density using the diagonal length of the bounding box as the numerator and the method of estimating the density based on the maximum axis length and the number of points of the bounding box. The automatic_nn_range_method_type field equal to 10 may indicate a calculation method combining the method of estimating the density using the diagonal length of the bounding box as the numerator and the method of estimating the density based on the minimum axis length of the bounding box and the number of points. The automatic_nn_range_method_type field equal to 11 may indicate the method of estimating the density using the diagonal length of the bounding box as the numerator and the method of estimating the density based on the middle axis length of the bounding box and the number of points.

The automatic_max_nn_range_in_table field may indicate the number of entries in the table of values of Kn in compressing the i-th attribute of the sequence.

The APS according to embodiments may include an iteration statement iterated as many times as the value of the automatic_max_nn_range_in_table field. In this case, according to an embodiment, j is initialized to 0 and is incremented by 1 each time the iteration statement is executed. The iteration statement is iterated until the value of j becomes the value of the automatic_max_nn_range_in_table field. This iteration statement may include an automatic_nn_range_table_k[j] field.

The automatic_nn_range_table_k[j] field may indicate a value of Kn in compressing the i-th attribute of the corresponding sequence.

According to embodiments, when the value of the different_nn_range_per_lod_flag field is TRUE, the APS further includes an iteration statement iterated as many times as the value of the lifting_num_detail_levels_minus1 field. In this case, according to an embodiment, the index (idx) is initialized to 0 and is incremented by 1 each time the iteration statement is executed. The iteration statement is iterated until the index (idx) is greater than the value of the lifting_num_detail_levels_minus1 field. This iteration statement may further include a nearest_neighbour_max_range [idx] field, a nearest_neighbour_min_range [idx] field, an nn_base_distance_calculation_method_type [idx] field, an nn_range_filtering_location_type [idx] field, and an automatic_nn_range_calculation_flag [idx] field.

The nearest_neighbour_max_range [idx] field may indicate the maximum neighbor point range for LOD idx. According to embodiments, the nearest_neighbour_max_range [idx] field may be used to limit the distance of a point registered as a neighbor for LOD idx. According to embodiments, the value of the nearest_neighbour_max_range [idx] field may be used as a value of NN_range for LOD idx.

The nearest_neighbour_min_range [idx] field may indicate the minimum neighbor point range for LOD idx.

The nn_base_distance_calculation_method_type [idx] field may indicate a base neighbor point distance calculation method for LOD idx. For the values assigned to the nn_base_distance_calculation_method_type [idx] field and the definition (or meaning) of the values, refer to the description of the nn_base_distance_calculation_method_type field.

According to embodiments, when the value of the nn_base_distance_calculation_method_type [idx] field is 0, that is, the field indicates use of the input base distance, the iteration statement may further include an nn_base_distance [idx] field.

The nn_base_distance [idx] field may specify a base neighbor point distance for LOD idx.

The nn_range_filtering_location_type [idx] field may indicate a method of applying the maximum neighbor point distance for LOD idx. For example, when the value of the nn_range_filtering_location_type [idx] field is 0, it may indicate a method by which a distance between points is calculated and a point outside the maximum neighbor point distance is not selected in selecting neighbor points. As another example, when the value of the nn_range_filtering_location_type [idx] field is 1, it may indicate a method by which all neighbor points are registered by calculating a distance between the points, and points beyond the maximum neighbor point distance are removed among the registered points.

The automatic_nn_range_calculation_flag [idx] field may indicate whether to automatically calculate the maximum neighbor point range for LOD idx. For example, when the value of the automatic_nn_range_calculation_flag [idx] field is 0 (i.e., TRUE), it may indicate automatic calculation of the maximum neighbor point range.

According to embodiments, when the value of the automatic_nn_range_calculation_flag [idx] field is 0, that is, when the field indicates the automatic calculation of the maximum neighbor point range, the iteration statement may further include an automatic_nn_range_method_type [idx] field and an automatic_max_nn_range_in_table [idx] field.

The automatic_nn_range_method_type [idx] field may indicate a method of calculating the maximum neighbor point range in compressing a corresponding attribute. For the values assigned to the automatic_nn_range_method_type [idx] field and the definition (or meaning) of the value, refer to the description of the values, refer to the description of the automatic_nn_range_method_type field.

The automatic_max_nn_range_in_table [idx] field may indicate the number of entries in the table of values of Kn for LOD idx.

The APS according to embodiments may include an iteration statement iterated as many times as the value of the automatic_max_nn_range_in_table [idx] field. In this case, according to an embodiment, j is initialized to 0 and is incremented by 1 each time the iteration statement is executed. The iteration statement is iterated until the value of j becomes the value of the automatic_max_nn_range_in_table [idx] field. This iteration statement may include an automatic_nn_range_table_k [idx][j] field.

The automatic_nn_range_table_k [idx][j] field may indicate a value of Kn for LOD idx.

FIG. 38 shows an embodiment of a syntax structure of a tile parameter set (TPS) (tile_parameter_set( )) according to the present disclosure. According to embodiments, a TPS may be referred to as a tile inventory. The TPS according to the embodiments includes information related to each tile. In particular, in this example, the TPS includes neighbor point selection-related option information.

The TPS according to the embodiments includes a num_tiles field.

The num_tiles field indicates the number of tiles signaled for the bitstream. When not present, num_tiles is inferred to be 0.

The TPS according to the embodiments includes an iteration statement repeated as many times as the value of the num_tiles field. In an embodiment, i is initialized to 0, and is incremented by 1 each time the iteration statement is executed. The iteration statement is repeated until the value of i becomes equal to the value of the num_tiles field. The iteration statement may include a tile_bounding_box_offset_x[i] field, a tile_bounding_box_offset_y[i] field, a tile_bounding_box_offset_z[i] field, a tile_bounding_box_size_width[i] field, a tile_bounding_box_size_height[i] field, and a tile_bounding_box_size_depth[i] field.

The tile_bounding_box_offset_x[i] field indicates the x offset of the i-th tile in the Cartesian coordinates.

The tile_bounding_box_offset_y[i] field indicates the y offset of the i-th tile in the Cartesian coordinates.

The tile_bounding_box_offset_z[i] field indicates the z offset of the i-th tile in the Cartesian coordinates.

The tile_bounding_box_size_width[i] field indicates the width of the i-th tile in the Cartesian coordinates.

The tile_bounding_box_size_height[i] field indicates the height of the i-th tile in the Cartesian coordinates.

The tile_bounding_box_size_depth[i] field indicates the depth of the i-th tile in the Cartesian coordinates.

According to embodiments, the TPS may further include neighbor point selection-related option information as follows.

According to embodiments, the neighbor point selection-related option information may be included in the iteration statement iterated as many times as the value of the aforementioned num_tiles field as follows.

According to an embodiment, when a value of the different_nn_range_in_tile_flag field is TRUE, the iteration statement may further include a nearest_neighbour_max_range [i] field, a nearest_neighbour_min_range [i] field, an nn_base_distance_calculation_method_type [i] field, an nn_range_filtering_location_type [i] field, and a different_nn_range_in_slice_flag [i] field.

The nearest_neighbour_max_range [i] field may indicate the maximum neighbor point range of the i-th tile. According to embodiments, the nearest_neighbour_max_range [i] field may be used to limit the distance of a point registered as a neighbor. According to embodiments, the value of the nearest_neighbour_max_range [i] field may be used as a value of NN_range in Equation 5.

The nearest_neighbour_min_range [i] field may indicate the minimum neighbor point range of the i-th tile.

The nn_base_distance_calculation_method_type [i] field may indicate a method of calculating a base neighbor point distance of the i-th tile. For the values assigned to the nn_base_distance_calculation_method_type [i] field and the definition (or meaning) of the values, refer to the description of the nn_base_distance_calculation_method_type field of the APS.

According to embodiments, when the value of the nn_base_distance_calculation_method_type [i] field is 0, that is, he field indicates use of the input base distance, the iteration statement may further include an nn_base_distance [i] field.

The nn_base_distance [i] field may specify the base neighbor point distance of the i-th tile.

The nn_range_filtering_location_type [i] field may indicate a method of applying the maximum neighbor point distance in the i-th tile. For the values assigned to the nn_range_filtering_location_type [i] field and the definition (or meaning) of the values, refer to the description of the nn_range_filtering_location_type field of the APS.

The different_nn_range_in_slice_flag [i] field may specify whether a tile is using a different maximum/minimum neighbor point range for a partitioned slice from the tile.

When the value of the different_nn_range_in_slice_flag [i] field is TRUE, the iteration statement may further include a nearest_neighbour_offset_range_in_slice_flag[i] field and an automatic_nn_range_calculation_flag [i] field.

The nearest_neighbour_offset_range_in_slice_flag[i] field may indicate whether the maximum/minimum neighbor point range defined in a slice is indicated by a range offset in the maximum/minimum neighbor point range defined in the tile or by an absolute value.

The automatic_nn_range_calculation_flag [i] field may indicate whether to automatically calculate the maximum neighbor point range applied to the i-th tile. For example, when the value of the automatic_nn_range_calculation_flag [i] field is 0 (i.e., TRUE), it may indicate automatic calculation of the maximum neighbor point range.

According to embodiments, when the value of the automatic_nn_range_calculation_flag [i] field is 0, that is, when the field indicates the automatic calculation of the maximum neighbor point range, the iteration statement may further include an automatic_nn_range_method_type [i] field and an automatic_max_nn_range_in_table [i] field.

The automatic_nn_range_method_type [i] field may indicate a method of calculating the maximum neighbor point range for the i-th tile. For the values assigned to the automatic_nn_range_method_type [i] field and the definition (or meaning) of the values, refer to the description of the automatic_nn_range_method_type field of the APS.

The automatic_max_nn_range_in_table [i] field may indicate the number of entries in the table of values of Kn in the i-th tile.

The APS according to embodiments may include an iteration statement iterated as many times as the value of the automatic_max_nn_range_in_table [i] field. In this case, according to an embodiment, j is initialized to 0 and is incremented by 1 each time the iteration statement is executed. The iteration statement is iterated until the value of j becomes the value of the automatic_max_nn_range_in_table [i]. This iteration statement may include an automatic_nn_range_table_k[i][j] field.

The automatic_nn_range_table_k [i][j] field may indicate a value of Kn in the i-th tile.

FIG. 39 shows an embodiment of a syntax structure of a geometry slice bitstream( ) according to the present disclosure.

The geometry slice bitstream (geometry_slice_bitstream( )) according to the embodiments may include a geometry slice header (geometry_slice_header( )) and geometry slice data (geometry_slice_data( )).

FIG. 40 shows an embodiment of a syntax structure of the geometry slice header (geometry_slice_header( )) according to the present disclosure.

A bitstream transmitted by the transmission device (or a bitstream received by the reception device) according to the embodiments may contain one or more slices. Each slice may include a geometry slice and an attribute slice. The geometry slice includes a geometry slice header (GSH). The attribute slice includes an attribute slice header (ASH).

The geometry slice header (geometry_slice_header( )) according to embodiments may include a gsh_geom_parameter_set_id field, a gsh_tile_id field, a gsh_slice_id field, a gsh_max_node_size_log2 field, a gsh_numpoints field, and a byte_alignment( ) field.

When the value of the gps_box_present_flag field included in the GPS is ‘true’ (e.g., 1), and the value of the gps_gsh_box_log2_scale_present_flag field is ‘true’ (e.g., 1), the geometry slice header (geometry_slice_header( )) according to the embodiments may further include a gsh_box_log2_scale field, a gsh_box_origin_x field, a gsh_box_origin_y field, and a gsh_box_origin_z field.

The gsh_geom_parameter_set_id field specifies the value of the gps_geom_parameter_set_id of the active GPS.

The gsh_tile_id field specifies the value of the tile id that is referred to by the GSH.

The gsh_slice_id specifies id of the slice for reference by other syntax elements.

The gsh_box_log2_scale field specifies the scaling factor of the bounding box origin for the slice.

The gsh_box_origin_x field specifies the x value of the bounding box origin scaled by the value of the gsh_box_log2_scale field.

The gsh_box_origin_y field specifies the y value of the bounding box origin scaled by the value of the gsh_box_log2_scale field.

The gsh_box_origin_z field specifies the z value of the bounding box origin scaled by the value of the gsh_box_log2_scale field.

The gsh_max_node_size_log2 field specifies a size of a root geometry octree node.

The gsh_points_number field specifies the number of coded points in the slice.

FIG. 41 shows an embodiment of a syntax structure of geometry slice data (geometry_slice_data( )) according to the present disclosure. The geometry slice data (geometry_slice_data( )) according to the embodiments may carry a geometry bitstream belonging to a corresponding slice.

The geometry_slice_data( ) according to the embodiments may include a first iteration statement repeated as many times as by the value of MaxGeometryOctreeDepth. In an embodiment, the depth is initialized to 0 and is incremented by 1 each time the iteration statement is executed, and the first iteration statement is repeated until the depth becomes equal to MaxGeometryOctreeDepth. The first iteration statement may include a second loop statement repeated as many times as the value of NumNodesAtDepth. In an embodiment, nodeidx is initialized to 0 and is incremented by 1 each time the iteration statement is executed. The second iteration statement is repeated until nodeidx becomes equal to NumNodesAtDepth. The second iteration statement may include xN=NodeX[depth][nodeIdx], yN=NodeY[depth][nodeIdx], zN=NodeZ[depth][nodeIdx], and geometry_node(depth, nodeIdx, xN, yN, zN). MaxGeometryOctreeDepth indicates the maximum value of the geometry octree depth, and NumNodesAtDepth[depth] indicates the number of nodes to be decoded at the corresponding depth. The variables NodeX[depth][nodeIdx], NodeY[depth][nodeIdx], and NodeZ[depth][nodeIdx] indicate the x, y, z coordinates of the nodeIdx-th node in decoding order at a given depth. The geometry bitstream of the node of the depth is transmitted through geometry node(depth, nodeIdx, xN, yN, zN).

The geometry slice data (geometry_slice_data( )) according to the embodiments may further include geometry_trisoup_data( ) when the value of the log2_trisoup_node_size field is greater than 0. That is, when the size of the triangle nodes is greater than 0, a geometry bitstream subjected to trisoup geometry encoding is transmitted through geometry_trisoup_data( ).

FIG. 42 shows an embodiment of a syntax structure of attribute_slice_bitstream( ) according to the present disclosure.

The attribute_slice_bitstream (attribute_slice_bitstream( )) according to the embodiments may include an attribute slice header (attribute_slice_header( )) and attribute slice data (attribute_slice_data( )).

FIG. 43 shows an embodiment of a syntax structure of an attribute slice header (attribute_slice_header( )) according to the present disclosure. The attribute slice header according to the embodiments includes signaling information for a corresponding attribute slice. In particular, in this example, the attribute slice header includes neighbor point selection-related option information.

The attribute slice header (attribute_slice_header( )) according to the embodiments may include an ash_attr_parameter_set_id field, an ash_attr_sps_attr_idx field, and an ash_attr_geom_slice_id field.

When the value of the aps_slice_qp_delta_present_flag field of the APS is ‘true’ (e.g., 1), the attribute slice header (attribute_slice_header( )) according to the embodiments may further include an ash_qp_delta_luma field and an ash_qp_delta_chroma field.

The ash_attr_parameter_set_id field specifies a value of the aps_attr_parameter_set_id field of the current active APS (e.g., the aps_attr_parameter_set_id field included in the APS described in FIG. 37 ).

The ash_attr_sps_attr_idx field identifies an attribute set in the current active SPS. The value of the ash_attr_sps_attr_idx field is in the range from 0 to the sps_num_attribute_sets field included in the current active SPS.

The ash_attr_geom_slice_id field specifies the value of the gsh_slice_id field of the current geometry_slice_header.

The ash_qp_delta_luma field specifies a luma delta quantization parameter (qp) derived from the initial slice qp in the active attribute parameter set.

The ash_qp_delta_chroma field specifies the chroma delta qp derived from the initial slice qp in the active attribute parameter set.

The attribute slice header (attribute_slice_header( )) according to the embodiments may further include neighbor point selection-related option information as follows.

In an embodiment, when the value of the different_nn_range_in_slice_flag field is TRUE, the attribute slice header may further include a different_nn_range_per_lod_flag field. In an embodiment, the different_nn_range_in_slice_flag field is signaled in the TPS.

The different_nn_range_per_lod_flag field may specify whether to use a different maximum/minimum neighbor point range for each LOD.

For example, when the value of the different_nn_range_per_lod_flag field is FALSE, and the value of the nearest_neighbour_offset_range_in_slice_flag field is FALSE, the attribute slice header may further include a nearest_neighbour_absolute_max_range field, a nearest_neighbour_absolute_min_range field, an nn_base_distance_calculation_method_type field, an nn_range_filtering_location_type field, and an automatic_nn_range_calculation_flag field.

The nearest_neighbour_absolute_max_range field may indicate the maximum neighbor point range in comprising the attribute of a corresponding slice. According to embodiments, the nearest_neighbour_absolute_max_range field may be used to limit the distance of a point registered as a neighbor in the slice. According to embodiments, the value of the nearest_neighbour_absolute_max_range field may be used as a value of NN_range of the slice.

The nearest_neighbour_absolute_min_range field may indicate the minimum neighbor point range in compressing the attribute of the slice.

The nn_base_distance_calculation_method_type field may indicate a base neighbor point distance calculation method in compressing the attribute of the slice. For the values assigned to the nn_base_distance_calculation_method_type field and the definition (or meaning) of the values, refer to the description of the nn_base_distance_calculation_method_type field of the APS.

According to embodiments, when the value of the nn_base_distance_calculation_method_type field is 0, that is, the field indicates use of the input base distance, the iteration statement may further include an nn_base_distance field.

The nn_base_distance field may specify a base neighbor point distance in compressing the attribute of the slice.

The nn_range_filtering_location_type field may indicate a method of applying the maximum neighbor point distance in compressing the attribute of the slice. For the values assigned to the nn_range_filtering_location_type field and the definition (or meaning) of the values, refer to the description of the nn_range_filtering_location_type field of the APS.

The automatic_nn_range_calculation_flag field may indicate whether to automatically calculate the maximum neighbor point range in compressing the attribute of the slice. For example, when the value of the automatic_nn_range_calculation_flag field is 0 (i.e., TRUE), it may indicate automatic calculation of the maximum neighbor point range.

According to embodiments, when the value of the automatic_nn_range_calculation_flag field is 0, that is, when the field indicates the automatic calculation of the maximum neighbor point range, the iteration statement may further include an automatic_nn_range_method_type field and an automatic_max_nn_range_in_table field.

The automatic_nn_range_method_type field may indicate a method of calculating the maximum neighbor point range in compressing the attribute of the slice. For the values assigned to the automatic_nn_range_method_type field and the definition (or meaning) of the values, refer to the description of the automatic_nn_range_method_type field of the APS.

The automatic_max_nn_range_in_table field may indicate the number of entries in the table of values of Kn in the i-th tile.

According to embodiments, when the value of the different_nn_range_per_lod_flag field is FALSE and the value of the nearest_neighbour_offset_range_in_slice_flag field is TRUE, the attribute_slice_header may further include a nearest_neighbour_max_range_offset field, a nearest_neighbour_min_range_offset field, an nn_base_distance_calculation_method_type field, an nn_range_filtering_location_type field.

The nearest_neighbour_max_range_offset field may indicate a maximum neighbor point range offset in compressing the attribute of the slice. According to an embodiment, the reference of the maximum neighbor point range offset is the maximum neighbor point range of a tile to which the slice belongs. According to embodiments, the nearest_neighbour_max_range_offset field may be used to limit the distance of a point registered as a neighbor in the slice. According to embodiments, the value of the nearest_neighbour_max_range_offset field may be used as an offset of the value of NN_range of the slice.

The nearest_neighbour_min_range_offset field may indicate a neighbor point minimum range offset in compressing the attribute of the slice. According to an embodiment, the reference of the minimum neighbor point range offset is the minimum neighbor point range of a tile to which the slice belongs.

The nn_base_distance_calculation_method_type field may indicate a base neighbor point distance calculation method in compressing the attribute of the slice. For the values assigned to the nn_base_distance_calculation_method_type field and the definition (or meaning) of the values, refer to the description of the nn_base_distance_calculation_method_type field of the APS.

According to embodiments, when the value of the nn_base_distance_calculation_method_type field is 0, that is, the field indicates use of the input base distance, the iteration statement may further include an nn_base_distance field.

The nn_base_distance field may specify a base neighbor point distance in compressing the attribute of the slice.

The nn_range_filtering_location_type field may indicate a method of applying the maximum neighbor point distance in compressing the attribute of the slice. For the values assigned to the nn_range_filtering_location_type field and the definition (or meaning) of the values, refer to the description of the nn_range_filtering_location_type field of the APS.

According to embodiments, when the value of the different_nn_range_per_lod_flag field is TRUE and the value of the nearest_neighbour_offset_range_in_slice_flag field is FALSE, the attribute_slice_header further includes an iteration statement iterated as many times as the value of the lifting_num_detail_levels_minus1 field. In this case, according to an embodiment, the index (idx) is initialized to 0 and is incremented by 1 each time the iteration statement is executed. The iteration statement is iterated until the index (idx) is greater than the value of the lifting_num_detail_levels_minus1 field. This iteration statement may further include a nearest_neighbour_absolute_max_range[idx] field, a nearest_neighbour_absolute_min_range[idx] field, an nn_base_distance_calculation_method_type [idx] field, an nn_range_filtering_location_type [idx] field, an automatic_nn_range_calculation_flag [idx] field.

According to an embodiment, the lifting_num_detail_levels_minus1 field indicates the number of LODs for attribute coding, and is signaled in the APS.

The nearest_neighbour_absolute_max_range [idx] field may indicate the maximum neighbor point range for LOD idx in compressing the attribute of a slice. According to embodiments, the nearest_neighbour_absolute_max_range [idx] field may be used to limit the distance of a point registered as a neighbor for LOD idx in the slice. According to embodiments, the value of the nearest_neighbour_absolute_max_range [idx] field may be used as a value of NN_range for LOD idx of the slice.

The nearest_neighbour_absolute_min_range [idx] field may indicate the minimum neighbor point range for LOD idx in compressing the attribute of the slice.

The nn_base_distance_calculation_method_type [idx] field may indicate a base neighbor point distance calculation method for LOD idx. For the values assigned to the nn_base_distance_calculation_method_type [idx] field and the definition (or meaning) of the values, refer to the description of the nn_base_distance_calculation_method_type field of the APS.

According to embodiments, when the value of the nn_base_distance_calculation_method_type [idx] field is 0, that is, the field indicates use of the input base distance, the iteration statement may further include an nn_base_distance [idx] field.

The nn_base_distance [idx] field may specify a base neighbor point distance for LOD idx.

The nn_range_filtering_location_type [idx] field may indicate a method of applying the maximum neighbor point distance for LOD idx. For the values assigned to the nn_range_filtering_location_type [idx] field and the definition (or meaning) of the values, refer to the description of the nn_range_filtering_location_type field of the APS.

The automatic_nn_range_calculation_flag [idx] field may indicate whether to automatically calculate the maximum neighbor point range for LOD idx. For example, when the value of the automatic_nn_range_calculation_flag [idx] field is 0 (i.e., TRUE), it may indicate automatic calculation of the maximum neighbor point range.

According to embodiments, when the value of the automatic_nn_range_calculation_flag [idx] field is 0, that is, when the field indicates the automatic calculation of the maximum neighbor point range, the iteration statement may further include an automatic_nn_range_method_type [idx] field and an automatic_max_nn_range_in_table [idx] field.

The automatic_nn_range_method_type [idx] field may indicate may indicate a method of calculating the maximum neighbor point range in compressing a corresponding attribute. For the values assigned to the automatic_nn_range_method_type [idx] field and the definition (or meaning) of the values, refer to the description of the automatic_nn_range_method_type field of the APS.

The automatic_max_nn_range_in_table [idx] field may indicate the number of entries in the table of values of Kn for LOD idx.

The APS according to embodiments may include an iteration statement iterated as many times as the value of the automatic_max_nn_range_in_table [idx] field. In this case, according to an embodiment, j is initialized to 0 and is incremented by 1 each time the iteration statement is executed. The iteration statement is iterated until the value of j becomes the value of the automatic_max_nn_range_in_table [idx] field. This iteration statement may include an automatic_nn_range_table_k [idx][j] field.

The automatic_nn_range_table_k [idx][j] field may indicate a value of Kn for LOD idx.

According to embodiments, when the value of the different_nn_range_per_lod_flag field is TRUE, and the value of the nearest_neighbour_offset_range_in_slice_flag field is TRUE, the attribute_slice_header further includes an iteration statement iterated as many times as the value of the lifting_num_detail_levels_minus1 field. In this case, according to an embodiment, the index (idx) is initialized to 0 and is incremented by 1 each time the iteration statement is executed. The iteration statement is iterated until the index (idx) is greater than the value of the lifting_num_detail_levels_minus1 field. This iteration statement may include a nearest_neighbour_max_range_offset [idx] field, a nearest_neighbour_max_range_offset [idx] field, an nn_base_distance_calculation_method_type [idx] field, and an nn_range_filtering_location_type [idx] field.

According to an embodiment, the lifting_num_detail_levels_minus1 field indicates the number of LODs for attribute coding, and is signaled in the APS.

The nearest_neighbour_max_range_offset [idx] field may indicate a maximum neighbor point range offset for LOD idx in compressing the attribute of the slice. According to an embodiment, the reference of the maximum neighbor point range offset is the maximum neighbor point range of a tile to which the slice belongs. According to embodiments, the nearest_neighbour_max_range_offset [idx] field may be used to limit the distance of a point registered as a neighbor for LOD idx in the slice. According to embodiments, the value of the nearest_neighbour_max_range_offset [idx] field may be used as an offset of the value of NN_range for the LOD idx of the slice.

The nearest_neighbour_min_range_offset [idx] field may indicate a neighbor point minimum range offset for LOD idx in compressing the attribute of the slice. According to an embodiment, the reference of the minimum neighbor point range offset is the minimum neighbor point range of a tile to which the slice belongs.

The nn_base_distance_calculation_method_type [idx] field may indicate a base neighbor point distance calculation method for LOD idx. For the values assigned to the nn_base_distance_calculation_method_type [idx] field and the definition (or meaning) of the values, refer to the description of the nn_base_distance_calculation_method_type field of the APS.

According to embodiments, when the value of the nn_base_distance_calculation_method_type [idx] field is 0, that is, the field indicates use of the input base distance, the iteration statement may further include an nn_base_distance [idx] field.

The nn_base_distance [idx] field may specify a base neighbor point distance for LOD idx.

The nn_range_filtering_location_type [idx] field may indicate a method of applying the maximum neighbor point distance for LOD idx. For the values assigned to the nn_range_filtering_location_type [idx] field and the definition (or meaning) of the values, refer to the description of the nn_range_filtering_location_type field of the APS.

FIG. 44 shows an embodiment of a syntax structure of the attribute slice data (attribute_slice_data( )) according to the present disclosure. The attribute slice data (attribute_slice_data( )) according to the embodiments may carry an attribute bitstream belonging to a corresponding slice.

In the attribute slice data (attribute_slice_data( )) of FIG. 44 , dimension=attribute_dimension[ash_attr_sps_attr_idx] represents the attribute_dimension (attribute_dimension) of the attribute set identified by the ash_attr_sps_attr_idx field in the corresponding attribute_slice_header. The attribute_dimension refers to the number of components constituting an attribute. An attribute according to embodiments represent reflectance, color, or the like. Accordingly, the number of components varies among attributes. For example, an attribute corresponding to color may have three color components (e.g., RGB). Accordingly, an attribute corresponding to reflectance may be a mono-dimensional attribute, and the attribute corresponding to color may be a three-dimensional attribute.

The attributes according to the embodiments may be attribute-encoded on a dimension-by-dimension basis.

For example, the attribute corresponding to reflectance and the attribute corresponding to color may be attribute-encoded, respectively. According to embodiments, attributes may be attribute-encoded together regardless of dimensions. For example, the attribute corresponding to reflectance and the attribute corresponding to color may be attribute-encoded together.

In FIG. 44 , zerorun specifies the number of 0 prior to residual).

In FIG. 44 , i denotes an i-th point value of the attribute. According to an embodiment, the attr_coding_type field and the lifting_adaptive_prediction_threshold field are signaled in the APS.

MaxNumPredictors of FIG. 44 is a variable used in the point cloud data decoding process, and may be acquired based on the value of the lifting_adaptive_prediction_threshold field signaled in the APS as follows.

MaxNumPredictors=lifting_max_num_direct_predictors field+1

Here, the lifting_max_num_direct_predictors field indicates the maximum number of predictors to be used for direct prediction.

According to the embodiments, predIndex[i] specifies the predictor index (or prediction mode) to decode the i-th point value of the attribute. The value of predIndex[i] is in the range from 0 to the value of the lifting_max_num_direct_predictors field.

The variable MaxPredDiff[i] according to the embodiments may be calculated as follows.

minValue = maxValue = ã₀ for(j = 0; j < k; j++) { minValue = Min(minValue, ã_(j)) maxValue = Max(maxValue, ã_(j)) } MaxPredDiff[i] = maxValue − minValue;

Here, let k₁ be the set of the k-nearest neighbors of the current point i and let (ã_(j))_(j∈N) _(i) be their decoded/reconstructed attribute values. The number of nearest neighbors, k_(i) shall be in the range of 1 to lifting_numpred_nearest_neighbours. According to embodiments, the decoded/reconstructed attribute values of neighbors are derived according to the Predictive Lifting decoding process.

The lifting_numpred_nearest_neighbours field is signaled in the APS and indicates the maximum number of nearest neighbors to be used for prediction.

FIG. 45 is a flowchart of a method of transmitting point cloud data according to embodiments.

The point cloud data transmission method according to the embodiments may include a step 71001 of encoding geometry contained in the point cloud data, a step 71002 of encoding an attribute contained in the point cloud data based on input and/or reconstructed geometry, and a step 71003 of transmitting a bitstream including the encoded geometry, the encoded attribute, and signaling information.

The steps 71001 and 71002 of encoding the geometry and attribute contained in the point cloud data may perform some or all of the operations of the point cloud video encoder 10002 of FIG. 1 , the encoding process 20001 of FIG. 2 , the point cloud video encoder of FIG. 4 , the point cloud video encoder of FIG. 12 , the point cloud encoding process of FIG. 14 , the point cloud video encoder of FIG. 15 or the geometry encoder and the attribute encoder of FIG. 17 .

In an embodiment, step 71002 of encoding the attribute may include generating an LOD₁ set by applying at least one of an octree-based LOD generation method, a distance-based LOD generation method, or a sampling-based LOD generation method, searching for X (>0) NN points in a group having the same or lower LOD (i.e., a large distance between nodes) based on the LOD₁ set, and registering the X NN points as a neighbor point set in a predictor.

According to embodiments, step 71002 of encoding the attribute may configure the neighbor point set by applying a search range and/or a maximum neighbor point distance.

According to embodiments, step 71002 of encoding the attribute may obtain the maximum neighbor point distance by multiplying a base neighbor point distance by NN_range. NN_range is a range within which a neighbor point may be selected and is referred to as a maximum range within which a neighbor point may be selected, a maximum neighbor point range, a neighbor point range, or a nearest neighbor range.

For parts of the base neighbor point distance, the maximum neighbor point range, and the maximum neighbor point distance that are not described below, refer to the description given above with reference to FIGS. 15 to 29 .

According to embodiments, in operation 71002 of encoding an attribute, a base neighbor point distance may be obtained by applying at least one of an octree-based base neighbor point distance calculation, a distance-based base neighbor point distance calculation, a sampling-based base neighbor point distance calculation, a base neighbor point distance calculation based on the average difference in Morton code between LODs, a base neighbor point distance calculation based on an average distance difference between LODs, or a base neighbor point distance calculation according to an input base neighbor point distance.

According to embodiments, the base neighbor point distance calculated according to a base neighbor point distance calculation method may be applied to the calculation of the maximum neighbor point range and/or the maximum neighbor point distance. In addition, neighbor point selection-related option information including information related to the base neighbor point distance may be signaled and transmitted in signaling information.

According to embodiments, in operation 71002 of encoding the attribute, a maximum neighbor point range may be automatically or manually set according to characteristics of the content.

According to embodiments, in operation 71002 of encoding the attribute, the maximum neighbor point range may be automatically calculated by estimating a density rate. For details of the method of automatically calculating the maximum neighbor point range by estimating the density rate, refer to the description given above with reference to FIG. 26 and/or FIG. 27 . Neighbor point selection-related option information including information related to the maximum neighbor point range may be signaled and transmitted in signaling information.

According to embodiments, the neighbor point selection-related option information may include at least one of information about a base neighbor point distance calculation method (e.g., nn_base_distance_calculation_method_type), base neighbor point distance information (e.g., nn_base_distance), maximum neighbor point range information (e.g., nearest_neighbor_max_range), minimum neighbor point range information (e.g. nearest_neighbor_min_range), information about a method of applying the maximum neighbor point distance (e.g., nn_range_filtering_location_type), information about whether to automatically calculate the maximum neighbor point range (e.g. automatic_nn_range_calculation_flag), information about a method of calculating the maximum neighbor point range (e.g., automatic_nn_range_method_type), or information related to the value of Kn (e.g., automatic_max_nn_range_in_table, automatic_nn_range_table_k). According to embodiments, the neighbor point selection-related option information may further include information about the maximum number of points that may be set as neighbor points (e.g., lifting_num_pred_nearest_neighbours), search range related information (e.g., lifting_search_range), and/or an LOD configuration method. In the present disclosure, for simplicity, at least one of information about the base neighbor point distance calculation method (e.g., nn_base_distance_calculation_method_type) and the base neighbor point distance information (e.g., nn_base_distance) may be referred to as base neighbor point distance related information.

According to an embodiment, step 71002 of encoding the attribute includes searching for X (e.g., 3) NN points among points within the search range in a group having the same or lower LOD (i.e., a large distance between nodes) based on the LOD₁ set as illustrated in FIG. 28 . Then, only NN points within the maximum neighbor point distance among the X (e.g., 3) NN points may be registered as the neighbor point set. Referring to FIG. 28 as an example, step 71002 of encoding the attribute includes comparing distance values between points within an actual search range and the point Px to search for X NN points and registering only points within the maximum neighbor point distance at an LOD to which the point Px belongs among the X points as the neighbor point set of the point Px. That is, the neighbor points registered as the neighbor point set of the point Px are limited to points within the maximum neighbor point distance at the LOD to which the point Px belongs among the X points.

According to another embodiment, step 71002 of encoding the attribute may include, as illustrated in FIG. 29 , searching for X (e.g., 3) NN points within the maximum neighbor point distance among points within the search range in a group having the same or lower LOD (i.e., a large distance between nodes) based on the LOD₁ set and registering the X (e.g., 3) NN points as the neighbor point set. Referring to FIG. 29 as an example, step 71002 of encoding the attribute includes comparing the distance values between the points within the actual search range and the point Px to search for X (e.g., 3) NN points within the maximum neighbor point distance at the LOD to which the point Px belongs from among points in the actual search range and registering the X NN points as the neighbor point set of the point Px. That is, the neighbor points registered as the neighbor point set of the point Px are limited to points within the maximum neighbor point distance at the LOD to which the point Px belongs.

According to embodiments, step 71002 of encoding the attribute includes acquiring a prediction attribute value of each point by applying one of prediction modes 0 to 3 when one or more neighbor points are registered in the predictor of each point and acquiring residual attribute values of points based on an original attribute value and the predication attribute value of each point.

According to embodiments, prediction mode 0 is a mode that calculates the prediction attribute value through a weighted average, prediction mode 1 is a mode that determines an attribute of a first neighbor point as the prediction attribute value, prediction mode 2 is a mode that determines an attribute of a second neighbor point as the prediction attribute value, and prediction mode 3 is a mode that determines an attribute of a third neighbor point as the prediction attribute value.

According to embodiments, in step 71002 of encoding the attribute, if a maximum difference value between attribute values of neighbor points registered in the predictor of a corresponding point is less than a preset threshold, prediction mode 0 is configured as a predication mode of the point. If the maximum difference value is equal to or greater than the preset threshold value, an RDO method is applied to a plurality of candidate prediction modes and one of the candidate prediction modes is configured as the prediction mode of the point. In an embodiment, this process is performed upon each point.

According to embodiments, a prediction mode applied to each point may be transmitted in attribute slice data.

According to embodiments, the step 71002 may apply a quantization and a zero-run length coding to the residual attribute values.

In the steps 71001 and 71002 according to embodiments, encoding may be performed on the basis of a slice or a tile containing one or more slices.

The step 71003 may be performed by the transmitter 10003 of FIG. 1 , the transmitting process 20002 of FIG. 2 , transmission processor 12012 of FIG. 12 or transmission processor 51008 of FIG. 15 .

FIG. 46 is a flowchart of a method of receiving point cloud data according to embodiments.

According to embodiments, a point cloud data reception method may include a step 81001 of receiving encoded geometries, encoded attributes, and signaling information, a step 81002 of decoding the geometries based on the signaling information, a step 81003 of decoding the attributes based on the signaling information and the decoded/reconstructed geometries, and a step 81004 of rendering point cloud data restored based on the decoded geometries and the decoded attributes.

The step 81001 according to embodiments may be performed by the receiver 10005 of FIG. 1 , the transmitting process 20002 or the decoding process 20003 of FIG. 2 , the receiver 13000 or the reception processor 13001 of FIG. 13 or the reception processor 61001 of FIG. 20 .

In the steps 81002 and 81003 according to embodiments, decoding may be performed on the basis of a slice or a tile containing one or more slices.

According to embodiments, the step 81002 may perform some or all of the operations of the point cloud video decoder 10006 of FIG. 1 , the decoding process 20003 of FIG. 2 , the point cloud video decoder of FIG. 11 , the point cloud video decoder of FIG. 13 , the geometry decoder of FIG. 20 or the geometry decoder of FIGS. 21A and 21B.

According to embodiments, the step 81003 may perform some or all of the operations of the point cloud video decoder 10006 of FIG. 1 , the decoding process 20003 of FIG. 2 , the point cloud video decoder of FIG. 11 , the point cloud video decoder of FIG. 13 , the attribute decoder of FIG. 30 or the attribute decoder of FIG. 31 .

According to embodiments, signaling information, for example, at least one of an SPS, an APS, a TPS, or an attribute slice header, may include neighbor point selection-related option information. According to embodiments, the neighbor point selection-related option information may include information related to NN_range (e.g., nearest_neighbor_max_range field). According to embodiments, the neighbor point selection-related option information may further include at least one of information about the maximum number of points that may be set as neighbor points (e.g., lifting_num_pred_nearest_neighbours field), information related to a search range (e.g., lifting_search_range field), and information about an LOD configuration method, or information about a base neighbor point distance.

In an embodiment, step 81003 of decoding the attribute may include generating an LOD₁ set by applying at least one of an octree-based LOD generation method, a distance-based LOD generation method, or a sampling-based LOD generation method, searching for X (>0) NN points in a group having the same or lower LOD (i.e., a large distance between nodes) based on the LOD₁ set, and registering the X NN points as a neighbor point set in the predictor. In an embodiment, the LOD generation method is signaled in signaling information (e.g., APS).

According to embodiments, step 81003 of decoding the attribute may configure the neighbor point set by applying a search range and/or a maximum neighbor point distance.

According to embodiments, step 81003 of encoding the attribute may obtain the maximum neighbor point distance by multiplying a base neighbor point distance by NN_range. NN_range is a range in which a neighbor point may be selected and is referred to as a maximum range in which a neighbor point may be selected, a maximum neighbor point range, a neighbor point range, or an NN_range.

For parts of the search range, the base neighbor point distance, the maximum neighbor point range, and the maximum neighbor point distance that are not described below, refer to the description given above with reference to FIGS. 15 to 31 .

According to embodiments, in operation 81003 of decoding an attribute, a base neighbor point distance may be acquired based on information related to the base neighbor point distance included in the neighbor point selection-related option information in the signaling information.

According to embodiments, in operation 81003 of decoding the attribute, the maximum neighbor point range may be may automatically or manually set according to the characteristics of the content. According to embodiments, in operation 81003 of decoding the attribute, the neighbor point selection-related option information included in the signaling information may be used to automatically or manually set the maximum neighbor point range according to the characteristics of the content.

According to embodiments, in operation 81003 of decoding the attribute, the maximum neighbor point range may be acquired directly from the neighbor point selection-related option information. Alternatively, the maximum neighbor point range may be automatically calculated based on the neighbor point selection-related option information.

According to embodiments, in operation 81003 of decoding the attribute, the maximum neighbor point range (NN_range) may be automatically calculated according to information about whether to automatically calculate the maximum neighbor point range (e.g., automatic_nn_range_calculation_flag) included in the neighbor point selection-related option information. For example, when the information about whether to automatically calculate the maximum range (e.g., automatic_nn_range_calculation_flag) indicates automatic calculation, the maximum neighbor point range (NN_range) may be automatically calculated based on information related to the base neighbor point distance, information about the method of calculating the maximum neighbor point range, and/or information related to the value of Kn as included in the neighbor point selection-related option information.

According to an embodiment, step 81003 of decoding the attribute includes searching for X (e.g., 3) NN points among points within the search range in a group having the same or lower LOD (i.e., a large distance between nodes) based on the LOD₁ set as illustrated in FIG. 28 . Then, only NN points within the maximum neighbor point distance among the X (e.g., 3) NN points may be registered as the neighbor point set. Referring to FIG. 28 as an example, step 81003 of decoding the attribute includes comparing distance values between points within an actual search range and the point Px to search for X NN points and registering only points within the maximum neighbor point distance at an LOD to which the point Px belongs among the X points as the neighbor point set of the point Px. That is, the neighbor points registered as the neighbor point set of the point Px are limited to points within the maximum neighbor point distance at the LOD to which the point Px belongs among the X points.

According to another embodiment, step 81003 of decoding the attribute may include, as illustrated in FIG. 29 , searching for X (e.g., 3) NN points within the maximum neighbor point distance among points within the search range in a group having the same or lower LOD (i.e., a large distance between nodes) based on the LOD₁ set and registering the X (e.g., 3) NN points as the neighbor point set. Referring to FIG. 29 as an example, step 81003 of decoding the attribute includes comparing the distance values between the points within the actual search range and the point Px to search for X (e.g., 3) NN points within the maximum neighbor point distance at the LOD to which the point Px belongs from points in the actual search range and registering the X NN points as the neighbor point set of the point Px. That is, neighbor points registered as the neighbor point set of the point Px are limited to points within the maximum neighbor point distance at the LOD to which the point Px belongs.

According to embodiments, step 81003 of decoding the attribute may include acquiring a prediction attribute value of a corresponding point by applying one of prediction modes 0 to 3 when one or more neighbor points are registered in the predictor of a specific point.

According to embodiments, prediction mode 0 is a mode that calculates a prediction attribute value through a weighted average, prediction mode 1 is a mode that determines an attribute of a first neighbor point as the prediction attribute value, prediction mode 2 is a mode that determines an attribute of a second neighbor point as the prediction attribute value, and prediction mode 3 is a mode that determines an attribute of a third neighbor point as the prediction attribute value.

According to embodiments, a prediction mode of a specific point may be configured as a default and predictor index information (predIndex) indicating the prediction mode may be signaled in attribute slice data.

According to an embodiment, the step 81003 may predict an attribute value of a point to be decoded based on the prediction mode 0 when the predictor index information of the point is not signaled in the attribute slice data.

According to an embodiment, the step 81003 may predict an attribute value of a point to be decoded based on a prediction mode that is signaled in the attribute slice data when the predictor index information of the point is signaled in the attribute slice data.

According to an embodiment, the step 81003 may restore an attribute value of the point by adding the predicted attribute value of the point and the received residual attribute value of the point. In an embodiment, an attribute value of each point may be restored by performing this process for each point.

According to an embodiment, the step 81003 may perform a zero-run length decoding on the received residual attribute values, which is an inverse process of a zero-run length encoding of a transmitting side, prior to restore the attribute values when the received residual attribute values are zero-run length encoded.

In the step 81004 of rendering the point cloud data according to the embodiments, the point cloud data may be rendered according to various rendering methods. For example, the points of the point cloud content may be rendered onto a vertex having a certain thickness, a cube of a specific minimum size centered on the vertex position, or a circle centered on the vertex position. All or part of the rendered point cloud content is provided to the user through a display (e.g. a VR/AR display, a general display, etc.).

The step 81004 according to the embodiments may be performed by the renderer 10007 of FIG. 1 , the rendering process 20004 of FIG. 2 , or the renderer 13011 of FIG. 13 .

As described above, according to the present disclosure, selection of meaningless neighbor points is excluded and meaningful neighbor points may be selected when configuring a neighbor point set by considering an attribute correlation between points of content during attribute encoding of point cloud content. Then, since a residual attribute value is reduced and a bitstream size is thereby reduced, compression efficiency of attributes is improved. In other words, in the present disclosure, compression efficiency of attributes may be improved using a method of restricting points that may be selected as the neighbor point set in consideration of the attribute correlation between points of content.

A point cloud data transmission method, a point cloud data transmission device, a point cloud data reception method, and a point cloud data reception device according to embodiments may provide a good-quality point cloud service.

A point cloud data transmission method, a point cloud data transmission device, a point cloud data reception method, and a point cloud data reception device according to embodiments may achieve various video codec methods.

A point cloud data transmission method, a point cloud data transmission device, a point cloud data reception method, and a point cloud data reception device according to embodiments may provide universal point cloud content such as a self-driving service (or an autonomous driving service).

A point cloud data transmission method, a point cloud data transmission device, a point cloud data reception method, and a point cloud data reception device according to embodiments may perform space-adaptive partition of point cloud data for independent encoding and decoding of the point cloud data, thereby improving parallel processing and providing scalability.

A point cloud data transmission method, a point cloud data transmission device, a point cloud data reception method, and a point cloud data reception device according to embodiments may perform encoding and decoding by spatially partitioning the point cloud data in units of tiles and/or slices, and signal necessary data therefore, thereby improving encoding and decoding performance of the point cloud.

A point cloud data transmission method and apparatus, and a point cloud data reception method and apparatus according to embodiments reduce the size of an attribute bitstream and enhance compression efficiency of attributes by selecting neighbor points used for attribute prediction in consideration of an attribute correlation between points of content when attribute information of G-PCC is encoded.

According to embodiments, a point cloud data transmission method, a point cloud data transmission device, a point cloud data reception method, and a point cloud data reception device may cause neighbor points for attribute prediction to be selected based on the maximum neighbor point distance in encoding attribute information of G-PCC, thereby reducing the size of the attribute bitstream and increasing the attribute compression efficiency.

According to embodiments, a point cloud data transmission method, a point cloud data transmission device, a point cloud data reception method, and a point cloud data reception device may cause neighbor points for attribute prediction to be selected based on the maximum distance of the neighbor points in encoding attribute information of G-PCC, thereby removing points beyond the maximum neighbor point distance, that is, points interfere with prediction from the neighbor point set. Accordingly, when the relevance of the attribute is low due to the attribute characteristics of the content, the average value of the prediction may not be increased to increase the residual value with regard to the point attribute value, and no weight may be assigned to unimportant information. Therefore, the attribute bitstream size may be reduced and PSNR accuracy may be increased.

According to embodiments, a point cloud data transmission method, a point cloud data transmission device, a point cloud data reception method, and a point cloud data reception device may configure the maximum range of neighbor points according to the LOD configuration method, service characteristics, or content characteristics. Accordingly, the maximum neighbor point range suitable for the attribute characteristics may be provided.

According to embodiments, a point cloud data transmission method, a point cloud data transmission device, a point cloud data reception method, and a point cloud data reception device may configure the maximum range of neighbor points according to the LOD configuration method, service characteristics, or content characteristics. Accordingly, various types of point cloud data may be efficiently encoded/decoded.

According to embodiments, a point cloud data transmission method, a point cloud data transmission device, a point cloud data reception method, and a point cloud data reception device may automatically calculate the maximum range of neighbor points according to density, thereby provide optimal compression efficiency.

According to embodiments, a point cloud data transmission method, a point cloud data transmission device, a point cloud data reception method, and a point cloud data reception device may estimate the maximum neighbor point distance using at least one of octree-based calculation of the maximum neighbor point distance, distance-based calculation of the maximum neighbor point distance, sampling-based calculation of the maximum neighbor point distance, calculation of the maximum neighbor point distance through calculation of the difference in Molton code average between LODs, or calculation of the maximum neighbor point distance through calculation of the difference in average distance between LODs, signal related information. Thereby, the attribute compression/decompression efficiency may be increased with the optimal set of neighbor points.

Each part, module, or unit described above may be a software, processor, or hardware part that executes successive procedures stored in a memory (or storage unit). Each of the steps described in the above embodiments may be performed by a processor, software, or hardware parts. Each module/block/unit described in the above embodiments may operate as a processor, software, or hardware. In addition, the methods presented by the embodiments may be executed as code. This code may be written on a processor readable storage medium and thus read by a processor provided by an apparatus.

In the specification, when a part “comprises” or “includes” an element, it means that the part further comprises or includes another element unless otherwise mentioned. Also, the term “ . . . module(or unit)” disclosed in the specification means a unit for processing at least one function or operation, and may be implemented by hardware, software or combination of hardware and software.

Although embodiments have been explained with reference to each of the accompanying drawings for simplicity, it is possible to design new embodiments by merging the embodiments illustrated in the accompanying drawings. If a recording medium readable by a computer, in which programs for executing the embodiments mentioned in the foregoing description are recorded, is designed by those skilled in the art, it may fall within the scope of the appended claims and their equivalents.

The apparatuses and methods may not be limited by the configurations and methods of the embodiments described above. The embodiments described above may be configured by being selectively combined with one another entirely or in part to enable various modifications.

Although preferred embodiments have been described with reference to the drawings, those skilled in the art will appreciate that various modifications and variations may be made in the embodiments without departing from the spirit or scope of the disclosure described in the appended claims. Such modifications are not to be understood individually from the technical idea or perspective of the embodiments.

Various elements of the apparatuses of the embodiments may be implemented by hardware, software, firmware, or a combination thereof. Various elements in the embodiments may be implemented by a single chip, for example, a single hardware circuit. According to embodiments, the components according to the embodiments may be implemented as separate chips, respectively. According to embodiments, at least one or more of the components of the apparatus according to the embodiments may include one or more processors capable of executing one or more programs. The one or more programs may perform any one or more of the operations/methods according to the embodiments or include instructions for performing the same. Executable instructions for performing the method/operations of the apparatus according to the embodiments may be stored in a non-transitory CRM or other computer program products configured to be executed by one or more processors, or may be stored in a transitory CRM or other computer program products configured to be executed by one or more processors. In addition, the memory according to the embodiments may be used as a concept covering not only volatile memories (e.g., RAM) but also nonvolatile memories, flash memories, and PROMs. In addition, it may also be implemented in the form of a carrier wave, such as transmission over the Internet. In addition, the processor-readable recording medium may be distributed to computer systems connected over a network such that the processor-readable code may be stored and executed in a distributed fashion.

In this document, the term “/” and “,” should be interpreted as indicating “and/or.” For instance, the expression “A/B” may mean “A and/or B.” Further, “A, B” may mean “A and/or B.” Further, “AB/C” may mean “at least one of A, B, and/or C.” “A, B, C” may also mean “at least one of A, B, and/or C.” Further, in the document, the term “or” should be interpreted as “and/or.” For instance, the expression “A or B” may mean 1) only A, 2) only B, and/or 3) both A and B. In other words, the term “or” in this document should be interpreted as “additionally or alternatively.”

Terms such as first and second may be used to describe various elements of the embodiments. However, various components according to the embodiments should not be limited by the above terms. These terms are only used to distinguish one element from another. For example, a first user input signal may be referred to as a second user input signal. Similarly, the second user input signal may be referred to as a first user input signal. Use of these terms should be construed as not departing from the scope of the various embodiments. The first user input signal and the second user input signal are both user input signals, but do not mean the same user input signal unless context clearly dictates otherwise. The terminology used to describe the embodiments is used for the purpose of describing particular embodiments only and is not intended to be limiting of the embodiments. As used in the description of the embodiments and in the claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. The expression “and/or” is used to include all possible combinations of terms. The terms such as “includes” or “has” are intended to indicate existence of figures, numbers, steps, elements, and/or components and should be understood as not precluding possibility of existence of additional existence of figures, numbers, steps, elements, and/or components.

As used herein, conditional expressions such as “if” and “when” are not limited to an optional case and are intended to be interpreted, when a specific condition is satisfied, to perform the related operation or interpret the related definition according to the specific condition. Embodiments may include variations/modifications within the scope of the claims and their equivalents. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Furthermore, operations according to embodiments describing in the present document may be performed by transmitting/receiving devices including a memory and/or a processor. The memory may store programs to process/control operations according to embodiments and the processor may control variable operations describing in the present document. The processor may be called a controller, etc. Operations according to embodiments may be implemented by firmware, software, and/or a combination thereof and the firmware, software, and/or a combination thereof may be stored in a processor or a memory. 

What is claimed is:
 1. A point cloud data transmission method, the method comprising: acquiring point cloud data; encoding geometry information including positions of points of the point cloud data; generating one or more levels of detail (LODs) based on the geometry information and selecting one or more nearest neighbor points of each point to be attribute-encoded based on the one or more LODs, wherein the selected one or more nearest neighbor points of each point are located within a maximum nearest neighbor point distance, wherein the maximum nearest neighbor point distance is obtained by multiplying a base distance by a maximum nearest neighbor point range, wherein the maximum nearest neighbor point range is calculated according to a value of a density of the point cloud data, and wherein the value of the density of the point cloud data is estimated based on a distance for attribute coding and a bounding box of the point cloud data; encoding attribute information of each point based on the selected one or more nearest neighbor points of each point; and transmitting the encoded geometry information, the encoded attribute information, and signaling information, wherein the signaling information includes information related to the maximum nearest neighbor point range.
 2. The method of claim 1, wherein the distance for attribute coding is the base distance.
 3. The method of claim 2, wherein the value of the density of the point cloud data is estimated by dividing the base distance by a diagonal length of the bounding box of the point cloud data.
 4. The method of claim 1, wherein the maximum nearest neighbor point range is a number of nodes of each point.
 5. The method of claim 1, wherein, when the one or more LODs are generated based on an octree, the base distance is determined based on a diagonal distance of one node at a specific LOD.
 6. A point cloud data transmission apparatus, the apparatus comprising: an acquisition unit configured to acquire point cloud data; a geometry encoder configured to encode geometry information including positions of points of the point cloud data; an attribute encoder configured to generate one or more levels of detail (LODs) based on the geometry information, select one or more nearest neighbor points of each point to be attribute encoded based on the one or more LODs, and encode attribute information of each point based on the selected one or more nearest neighbor points of each point, wherein the selected one or more nearest neighbor points of each point are located within a maximum nearest neighbor point distance, wherein the maximum nearest neighbor point distance is obtained by multiplying a base distance by a maximum nearest neighbor point range, wherein the maximum nearest neighbor point range is calculated according to a value of a density of the point cloud data, and wherein the value of the density of the point cloud data is estimated based on a distance for attribute coding and a bounding box of the point cloud data; and a transmitter configured to transmit the encoded geometry information, the encoded attribute information, and signaling information, wherein the signaling information includes information related to the maximum nearest neighbor point range.
 7. The apparatus of claim 6, wherein the distance for attribute coding is the base distance.
 8. The apparatus of claim 7, wherein the value of the density of the point cloud data is estimated by dividing the base distance by a diagonal length of the bounding box of the point cloud data.
 9. The apparatus of claim 6, wherein the maximum nearest neighbor point range is a number of nodes of each point.
 10. The apparatus of claim 6, wherein, when the one or more LODs are generated based on an octree, the base distance is determined based on a diagonal distance of one node at a specific LOD.
 11. A point cloud data reception apparatus, the apparatus comprising: a receiver configured to receive geometry information, attribute information, and signaling information; a geometry decoder configured to decode the geometry information based on the signaling information; an attribute decoder configured to decode the attribute information of each point based on one or more nearest neighbor points of each point and the signaling information, wherein the one or more nearest neighbor points of each point to be attributed decoded are selected based on one or more levels of detail (LODs), wherein the one or more LODs are generated based on the geometry information, wherein the selected one or more nearest neighbor points of each point are located within a maximum nearest neighbor point distance, wherein the maximum nearest neighbor point distance is obtained by multiplying a base distance by a maximum nearest neighbor point range, wherein the maximum nearest neighbor point range is calculated according to a value of a density of point cloud data, wherein the value of the density of the point cloud data is estimated based on a distance for attribute decoding and a bounding box of the point cloud data, and wherein the signaling information includes information related to the maximum nearest neighbor point range; and a renderer configured to render point cloud data restored based on the decoded geometry information and the decoded attribute information.
 12. The apparatus of claim 11, wherein the distance for attribute decoding is the base distance.
 13. The apparatus of claim 12, wherein the value of the density of the point cloud data is estimated by dividing the base distance by a diagonal length of the bounding box of the point cloud data.
 14. The apparatus of claim 11, wherein the maximum nearest neighbor point range is a number of nodes of each point.
 15. The apparatus of claim 11, wherein, when the one or more LODs are generated based on an octree, the base distance is determined based on a diagonal distance of one node at a specific LOD.
 16. A point cloud data reception method, the method comprising: receiving geometry information, attribute information, and signaling information; decoding the geometry information based on the signaling information; decoding the attribute information of each point based on one or more nearest neighbor points of each point and the signaling information, wherein the one or more nearest neighbor points of each point to be attributed decoded are selected based on one or more levels of detail (LODs), wherein the one or more LODs are generated based on the geometry information, wherein the selected one or more nearest neighbor points of each point are located within a maximum nearest neighbor point distance, wherein the maximum nearest neighbor point distance is obtained by multiplying a base distance by a maximum nearest neighbor point range, wherein the maximum nearest neighbor point range is calculated according to a value of a density of the point cloud data, wherein the value of the density of the point cloud data is estimated based on a distance for attribute decoding and a bounding box of the point cloud data, and wherein the signaling information includes information related to the maximum nearest neighbor point range; and rendering point cloud data restored based on the decoded geometry information and the decoded attribute information.
 17. The method of claim 16, wherein the distance for attribute decoding is the base distance.
 18. The method of claim 17, wherein the value of the density of the point cloud data is estimated by dividing the base distance by a diagonal length of the bounding box of the point cloud data.
 19. The method of claim 16, wherein the maximum nearest neighbor point range is a number of nodes of each point.
 20. The method of claim 16, wherein, when the one or more LODs are generated based on an octree, the base distance is determined based on a diagonal distance of one node at a specific LOD. 